diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,161 @@
+# hoauth2 Changelog
+
+## 2.15.1 (2026-04-17)
+- Dependency changes
+  - Relax the `containers` upper bound to `< 0.9` so `containers-0.8` is supported.
+  - No API or behavior changes.
+
+## 2.15.0 (2025-10-05)
+- Breaking changes
+  - Type and class renames
+    - `OAuth2Token` renamed to `TokenResponse`.
+    - `TokenRequestAuthenicationMethod` renamed to `ClientAuthenticationMethod`.
+    - `HasTokenRequestClientAuthenticationMethod` renamed to `HasClientAuthenticationMethod`.
+    - Removed several `Has*` type classes (e.g., `HasOAuth2Key`, `HasOAuthKey` from `HasTokenRequest`).
+  - Removed deprecated API in `Network.OAuth2.HttpClient`
+    - Deprecated functions have been removed. Use `authGetJSON`/`authGetBS`/`authPostJSON`/`authPostBS` and the `WithAuthMethod` variants with `APIAuthenticationMethod`.
+  - Request body encoding behavior
+    - `authPostJSON` now sends JSON with `Content-Type: application/json`. If an endpoint requires form-encoded data, use `authPostBS` or construct a custom request body.
+  - Import/module path cleanup
+    - Consumers should import `Network.OAuth2` (not `Network.OAuth.OAuth2`).
+- Behavioral changes and bug fixes
+  - Client authentication handling
+    - Append `client_id` and `client_secret` for `ClientSecretPost` in client credentials flow.
+    - Refresh token flow honors the configured client authentication method.
+    - Authorization Code flow supports client authentication methods.
+  - Device Authorization flow
+    - Updated handling of device authorization requests and polling behavior.
+- Refactors and internal cleanup
+  - Refactored header handling, simplified URI-to-Request conversion, removed deprecated or unused internals, and general cleanups.
+- Dependency changes
+  - Allow `microlens` 0.5 (`microlens` >= 0.4 && < 0.6).
+  - Raise lower bound to `uri-bytestring` >= 0.4 (< 0.5).
+
+## 2.14.3 (2025-03-14)
+
+- Fixes and improvements:
+  - Append client_id and client_secret for ClientSecretPost in client credentials flow
+  - Add raw response to token response and derive Show instances
+  - Skip empty scope; assorted refactors and cleanups
+
+## 2.14.2 (2025-01-30)
+
+* Updated uri-bytestring to version 0.4
+
+## 2.14.1 (2024-11-19)
+
+* Updated data-default to version 0.8
+
+## 2.14.0 (2024-11-19)
+
+* Updated crypton to version 1.0
+
+## 2.13.0 (2024-03-07)
+
+* Replaced cryptonite with crypton
+
+## 2.12.0 (2024-01-19)
+
+* Updated base64 to version 1.0
+
+## 2.11.0 (2023-12-30)
+
+* Updated aeson to version 2.2
+* Updated binary to version 0.10
+* Updated bytestring to version 0.12
+* Updated container to version 0.7
+
+## 2.10.0 (2023-11-17)
+
+* Added support for text 2.2
+
+## 2.9.0 (2023-10-26)
+
+* Refactored oauth2 Experiment module implementation
+* Removed generics
+* Added Device Authorization grant
+* Moved IdpName to hoauth2 and enabled DataKinds
+* Changed the type parameter in HttpClient methods
+* Removed data family `RefreshTokenRequest`
+
+## 2.8.1 (2023-06-17)
+
+* Added support for GHC-9.6
+* Updated CI configuration for GHC 9.6.1
+* Added hiedb integration
+
+## 2.8.0 (2023-03-15)
+
+* Added support for GHC-9.4.4
+* Added support for text-2.0
+
+## 2.7 (2022-11-17)
+
+* Added GrantType jwt-bearer
+* Added JWT authentication method for ClientCredential flow
+* Replaced `OAuth2Error` with `TokenRequestError`
+* Moved `HasIdpName` class to hoauth2-demo
+* Improved error handling when response body is empty in `HttpClient.handleResponse`
+* Removed the following modules from exposure list:
+    - Network.OAuth2.Experiment.Pkce
+    - Network.OAuth2.Experiment.Types
+    - Network.OAuth2.Experiment.Utils
+    - Network.OAuth.OAuth2.Internal
+
+## 2.6 (2022-10-04)
+
+* Changed type parameter order in http client JSON method
+* Modified http client to only accept one Authentication Method instead of a Set
+* Removed `authPostBS1` (non-standard approach to sending credentials)
+* Removed Douban IdP (discontinued OAuth2 support)
+* Deprecated all *Internal methods, added *WithAuthMethod alternatives
+* Changed license to MIT
+* Added support for PKCE flow in `Network.OAuth2.Experiment` module
+* Added support for Resource Owner Password and Client Credentials flows
+* Added `hoauth2-providers` and `hoauth2-providers-tutorial` modules
+* Added `hoauth2-tutorial` module
+
+## 2.5 (2022-08-17)
+
+* Updated aeson to version 2.1
+
+## 2.4 (2022-08-17)
+
+* Relaxed binary and bytestring version constraints
+
+## 2.1 (2022-02-19)
+
+* Added documentation for OAuth2 specification
+* Updated aeson to version 2
+
+## 2.0 (2022-02-15)
+
+* Breaking change: Refactored naming convention of `OAuth2` data type
+  ```diff
+  -  { oauthClientId            = "xxxxxxxxxxxxxxx"
+  -  , oauthClientSecret        = Just "xxxxxxxxxxxxxxxxxxxxxx"
+  -  , oauthCallback            = Just [uri|http://127.0.0.1:9988/oauthCallback|]
+  -  , oauthOAuthorizeEndpoint  = [uri|https://api.weibo.com/oauth2/authorize|]
+  -  , oauthAccessTokenEndpoint = [uri|https://api.weibo.com/oauth2/access_token|]
+  +  { oauth2ClientId           = "xxxxxxxxxxxxxxx"
+  +  , oauth2ClientSecret       = Just "xxxxxxxxxxxxxxxxxxxxxx"
+  +  , oauth2RedirectUri        = Just [uri|http://127.0.0.1:9988/oauthCallback|]
+  +  , oauth2AuthorizeEndpoint  = [uri|https://api.weibo.com/oauth2/authorize|]
+  +  , oauth2TokenEndpoint      = [uri|https://api.weibo.com/oauth2/access_token|]
+  +  }
+  ```
+
+## 1.7.0 (2018-03-03)
+
+* Added sample server and removed individual sample tests
+* Added `fetchAccessToken2` function
+* Added `refreshAccessToken` function and deprecated `fetchRefreshToken`
+* Renamed `authGetBS'` to `authGetBS2`
+* Renamed `authPostBS'` to `authPostBS2`
+* Added `authPostBS3` function
+
+## 1.0.0 (2017-04-07)
+
+* Added umbrella type `OAuth2Token` to accommodate `AccessToken` and `RefreshToken`
+* Typed the intermediate authentication code as `ExchangeToken`
+* Fixed missing client_id error in tests by appending client_id and client_secret to header
diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,30 +1,21 @@
-Copyright (c)2012, Haisheng Wu
-
-All rights reserved.
-
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are met:
+MIT License
 
-    * Redistributions of source code must retain the above copyright
-      notice, this list of conditions and the following disclaimer.
+Copyright (c) 2022 Haisheng Wu
 
-    * Redistributions in binary form must reproduce the above
-      copyright notice, this list of conditions and the following
-      disclaimer in the documentation and/or other materials provided
-      with the distribution.
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
 
-    * Neither the name of Haisheng Wu nor the names of other
-      contributors may be used to endorse or promote products derived
-      from this software without specific prior written permission.
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
 
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,13 +1,11 @@
-[![Build Status](https://secure.travis-ci.org/freizl/hoauth2.png?branch=master)](http://travis-ci.org/freizl/hoauth2)
-
-## Introduction
-
-A lightweight oauth2 haskell binding. See examples in `example/` folder.
-
-In additions, [snaplet-oauth] use this lib as well.
-
-[snaplet-oauth]: https://github.com/HaskellCNOrg/snaplet-oauth
-
-## Contribute
+Haskell bindings for
 
-Feel free send pull request or submit issue ticket.
+-   [The OAuth 2.0 Authorization Framework](https://datatracker.ietf.org/doc/html/rfc6749)
+    -   If the Identity Provider also implements [OIDC
+        spec](https://openid.net/specs/openid-connect-core-1_0.html), ID
+        Token will also be present in the token response (see
+        `TokenResponse`).
+-   [JWT Profile for OAuth2 Client Authentication and Authorization
+    Grants](https://www.rfc-editor.org/rfc/rfc7523.html)
+-   [The OAuth 2.0 Authorization Framework: Bearer Token
+    Usage](https://www.rfc-editor.org/rfc/rfc6750)
diff --git a/Setup.hs b/Setup.hs
deleted file mode 100644
--- a/Setup.hs
+++ /dev/null
@@ -1,2 +0,0 @@
-import Distribution.Simple
-main = defaultMain
diff --git a/example/Google/test.hs b/example/Google/test.hs
deleted file mode 100644
--- a/example/Google/test.hs
+++ /dev/null
@@ -1,85 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-{-
-
-This is basically very manual test. Check following link for details.
-
-google web oauth: https://developers.google.com/accounts/docs/OAuth2WebServer
-
-Google OAuth 2.0 playround: https://developers.google.com/oauthplayground/
-
--}
-
-module Main where
-
-import qualified Data.ByteString.Char8 as BS
-import Data.Maybe (fromJust)
-import Network.HTTP.Types (renderSimpleQuery, parseSimpleQuery)
-import System.Environment
-
-import Network.OAuth.OAuth2.HttpClient
-import Network.OAuth.OAuth2
-import Google.Key
-
-
---------------------------------------------------
-
-main :: IO ()
-main = do
-    (x:_) <- getArgs
-    case x of
-        "normal" -> normalCase
-        "offline" -> offlineCase
-
-
-offlineCase :: IO ()
-offlineCase = do 
-          print $ authorizationUrl googleKeys `BS.append` "&" `BS.append` extraParams
-          putStrLn "visit the url and paste code here: "
-          code <- getLine
-          (Just (AccessToken accessToken refreshToken)) <- requestAccessToken googleKeys (BS.pack code) 
-          print (accessToken, refreshToken)
-          validateToken accessToken >>= print
-          -- 
-          -- obtain a new access token with refresh token, which turns out only in response at first time.
-          -- Revoke Access https://www.google.com/settings/security
-          --
-          case refreshToken of
-            Nothing -> print "Failed to fetch refresh token"
-            Just tk -> refreshAccessToken googleKeys tk >>= print
-    where extraParams = renderSimpleQuery False $ ("access_type", "offline"):googleScopeEmail
-
-
-normalCase :: IO ()
-normalCase = do 
-          print $ authorizationUrl googleKeys `BS.append` "&" `BS.append` extraParams
-          putStrLn "visit the url and paste code here: "
-          code <- getLine
-          (Just (AccessToken accessToken Nothing)) <- requestAccessToken googleKeys (BS.pack code) 
-          print accessToken
-          res <- validateToken accessToken
-          print res
-          res2 <- userinfo accessToken
-          print res2
-    where extraParams = renderSimpleQuery False googleScopeEmail
-
-
---------------------------------------------------
--- Google API
-
--- | this is special for google Gain read-only access to the user's email address.
-googleScopeEmail = [("scope", "https://www.googleapis.com/auth/userinfo.email")]
-
--- | Gain read-only access to basic profile information, including a 
-googleScopeUserInfo = [("scope", "https://www.googleapis.com/auth/userinfo.profile")]
-
--- Token Validation
-validateToken accessToken = doSimplePostRequest ("https://www.googleapis.com/oauth2/v1/tokeninfo", 
-                                                 (accessTokenToParam accessToken))
-
--- | fetch user email.
---   for more information, please check the playround site.
---
-userinfo accessToken = doSimpleGetRequest (appendQueryParam
-                                           "https://www.googleapis.com/oauth2/v2/userinfo"
-	                                   (accessTokenToParam accessToken))
diff --git a/example/Weibo/test.hs b/example/Weibo/test.hs
deleted file mode 100644
--- a/example/Weibo/test.hs
+++ /dev/null
@@ -1,47 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE FlexibleContexts #-}
-
-{-
-
-weibo oauth2: http://open.weibo.com/wiki/Oauth2
-
-This is very trivial testing of the httpclient api.
-1. this case will print out a URL
-2. run the URL in browser and will navigate to weibo auth page
-3. conform the authentication and browser will navigate back to the callback url,
-   which obviously will failed cause there is no local server.
-4. copy the `code` in the callback url and parse into console
-5. this test case will gain access token using the `code` and print it out.
-
-check for integration testing at: 
-https://github.com/HaskellCNOrg/snaplet-oauth/tree/master/test
-
--}
-
-module Main where
-
-import qualified Data.ByteString as BS
-import qualified Data.ByteString.Lazy.Char8 as BSL
-import Data.Maybe (fromJust)
-import qualified Data.Text as T
-import qualified Data.Text.Encoding as T
-import qualified Network.HTTP.Types as HT
-import Network.HTTP.Conduit
-import Control.Monad.Trans.Control (MonadBaseControl)
-import Data.Conduit (MonadResource)
-
-import Network.OAuth.OAuth2.HttpClient
-import Network.OAuth.OAuth2
-
-import Weibo.Key
- 
-main :: IO ()
-main = do 
-          print $ authorizationUrl weiboKeys
-          putStrLn "visit the url and paste code here: "
-          code <- getLine
-          token <- requestAccessToken weiboKeys (sToBS code)
-          print token
-
-sToBS :: String -> BS.ByteString
-sToBS = T.encodeUtf8 . T.pack
diff --git a/hoauth2.cabal b/hoauth2.cabal
--- a/hoauth2.cabal
+++ b/hoauth2.cabal
@@ -1,67 +1,122 @@
-Name:                hoauth2
--- (http://www.haskell.org/haskellwiki/Package_versioning_policy)
-Version:             0.2.6
-
-Synopsis:            hoauth2
-Description:
-  Haskell OAuth2 authentication.
-  .
-  Tested following services
-  .
-  * google web oauth: <https://developers.google.com/accounts/docs/OAuth2WebServer>
-  .
-  * weibo oauth2: <http://open.weibo.com/wiki/Oauth2>
+cabal-version:      2.4
+name:               hoauth2
 
-Homepage:            https://github.com/freizl/hoauth2
-License:             BSD3
-License-file:        LICENSE
-Author:              Haisheng Wu
-Maintainer:          freizl@gmail.com
-Copyright:           Haisheng,Wu
-Category:            Network
-Build-type:          Simple
-stability:           alpha
-tested-with:         GHC <= 7.6.1
+-- http://wiki.haskell.org/Package_versioning_policy
+version:            2.15.1
+synopsis:           Haskell OAuth2 authentication client
+description:
+  This package provides Haskell bindings for the OAuth2 Authorization Framework and Bearer Token Usage.
 
+homepage:           https://github.com/freizl/hoauth2
+license:            MIT
+license-file:       LICENSE
+author:             Haisheng Wu
+maintainer:         Haisheng Wu <freizl@gmail.com>
+copyright:          Haisheng Wu
+category:           Network
+build-type:         Simple
+stability:          Beta
+tested-with:
+  GHC ==8.10.7 || ==9.0.2 || ==9.2.7 || ==9.4.4 || ==9.6.1 || ==9.8.2
 
--- Extra files to be distributed with the package, such as examples or
--- a README.
-Extra-source-files:
+extra-source-files:
+  CHANGELOG.md
   README.md
-  example/Google/test.hs
-  example/Weibo/test.hs
 
-Cabal-version:       >=1.8
+source-repository head
+  type:     git
+  location: https://github.com/freizl/hoauth2.git
 
-Source-Repository head
-  Type:     git
-  Location: git://github.com/freizl/hoauth2.git
+library
+  hs-source-dirs:     src
+  default-language:   Haskell2010
+  autogen-modules:    Paths_hoauth2
+  other-modules:
+    Network.HTTP.Client.Contrib
+    Network.OAuth2.Internal
+    Network.OAuth2.Experiment.Grants
+    Network.OAuth2.Experiment.Utils
+    Paths_hoauth2
 
+  exposed-modules:
+    Network.OAuth2
+    Network.OAuth2.AuthorizationRequest
+    Network.OAuth2.HttpClient
+    Network.OAuth2.TokenRequest
+    Network.OAuth2.Experiment
+    Network.OAuth2.Experiment.Flows
+    Network.OAuth2.Experiment.Flows.AuthorizationRequest
+    Network.OAuth2.Experiment.Flows.DeviceAuthorizationRequest
+    Network.OAuth2.Experiment.Flows.RefreshTokenRequest
+    Network.OAuth2.Experiment.Flows.TokenRequest
+    Network.OAuth2.Experiment.Flows.UserInfoRequest
+    Network.OAuth2.Experiment.Grants.AuthorizationCode
+    Network.OAuth2.Experiment.Grants.ClientCredentials
+    Network.OAuth2.Experiment.Grants.DeviceAuthorization
+    Network.OAuth2.Experiment.Grants.JwtBearer
+    Network.OAuth2.Experiment.Grants.ResourceOwnerPassword
+    Network.OAuth2.Experiment.Pkce
+    Network.OAuth2.Experiment.Types
 
-Library
-  hs-source-dirs: src
-  Exposed-modules:
-    Network.OAuth.OAuth2.HttpClient
-    Network.OAuth.OAuth2
+  default-extensions:
+    DeriveGeneric
+    GeneralizedNewtypeDeriving
+    ImportQualifiedPost
+    InstanceSigs
+    OverloadedStrings
+    PolyKinds
+    RecordWildCards
+    TypeFamilies
 
-  Build-Depends:
-    aeson             >= 0.6    && < 0.7,
-    base              >= 4      && < 5,
-    text              >= 0.11   && < 0.12,
-    bytestring        >= 0.9    && < 0.11,
-    bytestring-show   >= 0.3.5  && < 0.4,
-    conduit           >= 0.5    && < 0.6,
-    http-conduit      >= 1.8.4    && < 1.8.5,
-    http-types        >= 0.7    && < 0.8,
-    monad-control     >= 0.3    && < 0.4,
-    mtl               >= 1      && < 2.2,
-    transformers      >= 0.2    && < 0.4,
-    resourcet         >= 0.4.0.2 && < 0.4.1,
-    random
+  build-depends:
+    , aeson                 >=2.0    && <2.3
+    , base                  >=4.11   && <5
+    , base64                >=1.0    && <1.1
+    , binary                >=0.8    && <0.11
+    , binary-instances      >=1.0    && <1.1
+    , bytestring            >=0.9    && <0.13
+    , containers            >=0.6    && <0.9
+    , crypton               >=0.32   && <1.1
+    , data-default          ^>=0.8
+    , exceptions            >=0.8.3  && <0.11
+    , http-conduit          >=2.1    && <2.4
+    , http-types            >=0.11   && <0.13
+    , memory                ^>=0.18
+    , microlens             >=0.4 && <0.6
+    , text                  >=2.0    && <2.3
+    , transformers          >=0.4    && <0.7
+    , uri-bytestring        >=0.4    && <0.5
+    , uri-bytestring-aeson  ^>=0.1
 
-  if impl(ghc >= 6.12.0)
-      ghc-options: -Wall -fwarn-tabs -funbox-strict-fields
-                   -fno-warn-orphans -fno-warn-unused-do-bind
-  else
-      ghc-options: -Wall -fwarn-tabs -funbox-strict-fields
-                   -fno-warn-orphans
+  ghc-options:
+    -Wall -Wtabs -Wno-unused-do-bind -Wunused-packages -Wpartial-fields
+    -Wwarn -Wwarnings-deprecations
+
+test-suite hoauth-tests
+  type:               exitcode-stdio-1.0
+  main-is:            Spec.hs
+  hs-source-dirs:     test
+  ghc-options:        -Wall
+  build-depends:
+    , aeson           >=2.0  && <2.3
+    , base            >=4.11 && <5
+    , binary          >=0.8  && <0.11
+    , hoauth2
+    , hspec           >=2    && <3
+    , uri-bytestring  >=0.4  && <0.5
+    , http-conduit          >=2.1    && <2.4
+
+  other-modules:
+    Network.OAuth2.InternalSpec
+    Network.OAuth2.TokenRequestSpec
+    Network.OAuth2.TokenResponseSpec
+
+  default-language:   Haskell2010
+  default-extensions:
+    ImportQualifiedPost
+    OverloadedStrings
+
+  build-tool-depends: hspec-discover:hspec-discover >=2 && <3
+  ghc-options:
+    -Wall -Wtabs -Wno-unused-do-bind -Wunused-packages -Wpartial-fields
+    -Wwarn -Wwarnings-deprecations
diff --git a/src/Network/HTTP/Client/Contrib.hs b/src/Network/HTTP/Client/Contrib.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/HTTP/Client/Contrib.hs
@@ -0,0 +1,25 @@
+module Network.HTTP.Client.Contrib where
+
+import Data.Aeson
+import Data.Bifunctor
+import Data.ByteString.Lazy.Char8 qualified as BSL
+import Network.HTTP.Conduit
+import Network.HTTP.Types qualified as HT
+
+-- | Get response body out of a @Response@
+handleResponse :: Response BSL.ByteString -> Either BSL.ByteString BSL.ByteString
+handleResponse rsp
+  | HT.statusIsSuccessful (responseStatus rsp) = Right (responseBody rsp)
+  -- TODO: better to surface up entire resp so that client can decide what to do when error happens.
+  -- e.g. when 404, the response body could be empty hence library user has no idea what's happening.
+  -- Which will be breaking changes.
+  -- The current work around is surface up entire response as string.
+  | BSL.null (responseBody rsp) = Left (BSL.pack $ show rsp)
+  | otherwise = Left (responseBody rsp)
+
+handleResponseJSON ::
+  FromJSON a =>
+  Response BSL.ByteString ->
+  Either BSL.ByteString a
+handleResponseJSON =
+  either Left (first BSL.pack . eitherDecode) . handleResponse
diff --git a/src/Network/OAuth/OAuth2.hs b/src/Network/OAuth/OAuth2.hs
deleted file mode 100644
--- a/src/Network/OAuth/OAuth2.hs
+++ /dev/null
@@ -1,159 +0,0 @@
-{-# LANGUAGE DeriveDataTypeable #-}
-{-# LANGUAGE OverloadedStrings  #-}
-
--- | A simple OAuth2 Haskell binding.
---   (This is supposed to be independent with http client.)
-
-module Network.OAuth.OAuth2 where
-
-import           Control.Applicative ((<$>), (<*>))
-import           Control.Exception
-import           Control.Monad       (mzero)
-import           Data.Aeson
-import qualified Data.ByteString     as BS
-import           Data.Maybe          (fromMaybe)
-import           Data.Typeable       (Typeable)
-import           Network.HTTP.Types  (renderSimpleQuery)
-
---------------------------------------------------
--- Data Types
---------------------------------------------------
-
--- | Query Parameter Representation
---
-data OAuth2 = OAuth2 { oauthClientId            :: BS.ByteString
-                     , oauthClientSecret        :: BS.ByteString
-                     , oauthOAuthorizeEndpoint  :: BS.ByteString
-                     , oauthAccessTokenEndpoint :: BS.ByteString
-                     , oauthCallback            :: Maybe BS.ByteString
-                     , oauthAccessToken         :: Maybe BS.ByteString
-                       -- ^ TODO: why not Maybe AccessToken???
-                     } deriving (Show, Eq)
-
--- | Simple Exception representation.
-data OAuthException = OAuthException String
-                      deriving (Show, Eq, Typeable)
-
--- | OAuthException is kind of Exception.
---
-instance Exception OAuthException
-
--- | The gained Access Token. Use @Data.Aeson.decode@ to decode string to @AccessToken@.
---   The @refresheToken@ is special at some case.
---   e.g. https://developers.google.com/accounts/docs/OAuth2
---
-data AccessToken = AccessToken { accessToken  :: BS.ByteString
-                               , refreshToken :: Maybe BS.ByteString }
-                   deriving (Show)
-
--- | Parse JSON data into {AccessToken}
---
-instance FromJSON AccessToken where
-    parseJSON (Object o) = AccessToken
-                           <$> o .: "access_token"
-                           <*> o .:? "refresh_token"
-    parseJSON _ = mzero
-
---------------------------------------------------
--- Types Synonym
---------------------------------------------------
-
--- | type synonym of query parameters
-type QueryParams = [(BS.ByteString, BS.ByteString)]
-
--- | type synonym of post body content
-type PostBody = [(BS.ByteString, BS.ByteString)]
-
--- | type synonym of a URI
-type URI = BS.ByteString
-
--- | Access Code that is required for fetching Access Token
-type AccessCode = BS.ByteString
-
-
---------------------------------------------------
--- URLs
---------------------------------------------------
-
--- | Prepare the authorization URL.
---   Redirect to this URL asking for user interactive authentication.
---
-authorizationUrl :: OAuth2 -> URI
-authorizationUrl oa = oauthOAuthorizeEndpoint oa `appendQueryParam` queryStr
-  where queryStr = transform' [ ("client_id", Just $ oauthClientId oa)
-                              , ("response_type", Just "code")
-                              , ("redirect_uri", oauthCallback oa)]
-
-
--- | Prepare URL and the request body query for fetching access token.
---
-accessTokenUrl :: OAuth2
-                  -> AccessCode       -- ^ access code gained via authorization URL
-                  -> (URI, PostBody)  -- ^ access token request URL plus the request body.
-accessTokenUrl oa code = accessTokenUrl' oa code (Just "authorization_code")
-
-
-accessTokenUrl' ::  OAuth2
-                    -> AccessCode            -- ^ access code gained via authorization URL
-                    -> Maybe BS.ByteString   -- ^ Grant Type
-                    -> (URI, PostBody)       -- ^ access token request URL plus the request body.
-accessTokenUrl' oa code gt = (uri, body)
-  where uri  = oauthAccessTokenEndpoint oa
-        body = transform' [ ("client_id", Just $ oauthClientId oa)
-                          , ("client_secret", Just $ oauthClientSecret oa)
-                          , ("code", Just code)
-                          , ("redirect_uri", oauthCallback oa)
-                          , ("grant_type", gt) ]
-
--- | Using a Refresh Token.
---   obtain a new access token by sending a refresh token to the Authorization server.
---
-refreshAccessTokenUrl :: OAuth2
-                         -> BS.ByteString    -- ^ refresh token gained via authorization URL
-                         -> (URI, PostBody)  -- ^ refresh token request URL plus the request body.
-refreshAccessTokenUrl oa rtoken = (uri, body)
-  where uri = oauthAccessTokenEndpoint oa
-        body = transform' [ ("client_id", Just $ oauthClientId oa)
-                          , ("client_secret", Just $ oauthClientSecret oa)
-                          , ("grant_type", Just "refresh_token")
-                          , ("refresh_token", Just rtoken) ]
-
---------------------------------------------------
--- UTILs
---------------------------------------------------
-
--- | Append query parameters with '?'
-appendQueryParam :: URI -> QueryParams -> URI
-appendQueryParam uri q = uri `BS.append` renderSimpleQuery True q
-
--- | Append query parameters with '&'.
-appendQueryParam' :: URI -> QueryParams -> URI
-appendQueryParam' uri q = uri `BS.append` "&" `BS.append` renderSimpleQuery False q
-
--- | For GET method API.
-appendAccessToken :: URI   -- ^ Base URI
-          -> OAuth2        -- ^ OAuth has Authorized Access Token
-          -> URI           -- ^ Combined Result
-appendAccessToken uri oauth = appendQueryParam uri
-                              (token $ oauthAccessToken oauth)
-                              where token :: Maybe BS.ByteString -> QueryParams
-                                    token = accessTokenToParam . fromMaybe ""
-
--- | Create QueryParams with given access token value.
---
-accessTokenToParam :: BS.ByteString -> QueryParams
-accessTokenToParam token = [("access_token", token)]
-
-
--- | lift value in the Maybe and abonda Nothing
-transform' :: [(a, Maybe b)] -> [(a, b)]
-transform' = foldr step' []
-             where step' :: (a, Maybe b) -> [(a, b)] -> [(a, b)]
-                   step' (a, Just b) xs = (a, b):xs
-                   step' _ xs = xs
-
-
-                        -- Expect Access Token exists
-                        -- FIXME: append empty when Nothing
-  --uri `BS.append` renderSimpleQuery True (accessTokenToParam $ token oauth)
-
diff --git a/src/Network/OAuth/OAuth2/HttpClient.hs b/src/Network/OAuth/OAuth2/HttpClient.hs
deleted file mode 100644
--- a/src/Network/OAuth/OAuth2/HttpClient.hs
+++ /dev/null
@@ -1,128 +0,0 @@
-{-# LANGUAGE DeriveDataTypeable #-}
-{-# LANGUAGE FlexibleContexts   #-}
-{-# LANGUAGE OverloadedStrings  #-}
-
--- | A simple http client for request OAuth2 tokens and several utils.
-
-module Network.OAuth.OAuth2.HttpClient where
-
-import           Control.Exception
-import           Control.Monad                (liftM)
-import           Control.Monad.Trans.Resource (ResourceT)
-import           Data.Aeson
-import qualified Data.ByteString              as BS
-import qualified Data.ByteString.Lazy.Char8   as BSL
-import qualified Data.Text                    as T
-import qualified Data.Text.Encoding           as T
-import           Network.HTTP.Conduit
-import           Network.HTTP.Types           (renderSimpleQuery)
-import qualified Network.HTTP.Types           as HT
-
-import           Network.OAuth.OAuth2
-
---------------------------------------------------
--- Fetch AccessToken; RefreshAccessToken
---------------------------------------------------
-
--- | Request (via POST method) "Access Token".
---
---   FIXME: what if @requestAccessToken'@ return error?
---
-requestAccessToken :: OAuth2                 -- ^ OAuth Data
-                   -> BS.ByteString          -- ^ Authentication code gained after authorization
-                   -> IO (Maybe AccessToken) -- ^ Access Token
-requestAccessToken oa code = doJSONPostRequest (accessTokenUrl oa code)
-
-
--- | Request the "Refresh Token".
---
-refreshAccessToken :: OAuth2
-                   -> BS.ByteString          -- ^ refresh token gained after authorization
-                   -> IO (Maybe AccessToken)
-refreshAccessToken oa rtoken = doJSONPostRequest (refreshAccessTokenUrl oa rtoken)
-
-
---------------------------------------------------
--- conduit http request
---------------------------------------------------
-
--- | Conduct post request.
---
-doSimplePostRequest :: (URI, PostBody)       -- ^ The URI and request body for fetching token.
-                       -> IO BSL.ByteString  -- ^ Response as ByteString
-doSimplePostRequest (uri, body) = doPostRequst (bsToS uri) body >>= handleResponse
-
--- | Conduct post request and return response as JSON.
---
-doJSONPostRequest :: FromJSON a
-                     => (URI, PostBody)  -- ^ The URI and request body for fetching token.
-                     -> IO (Maybe a)     -- ^ Response as ByteString
-doJSONPostRequest (uri, body) = doPostRequst (bsToS uri) body
-                                >>= liftM decode . handleResponse
-
--- | Conduct GET request.
---
-doSimpleGetRequest :: URI                           -- ^ URL
-                      -> IO BSL.ByteString  -- ^ Response as ByteString
-doSimpleGetRequest url = doGetRequest (bsToS url) [] >>= handleResponse
-
--- | Conduct GET request and return response as JSON.
---
-doJSONGetRequest :: FromJSON a
-                    => URI         -- ^ Full URL
-                    -> IO (Maybe a)   -- ^ Response as ByteString
-doJSONGetRequest url = doGetRequest (bsToS url) []
-                       >>= liftM decode . handleResponse
-
-
--- | Conduct GET request with given URL by append extra parameters provided.
---
-doGetRequest :: String                               -- ^ URL
-                -> [(BS.ByteString, BS.ByteString)]  -- ^ Extra Parameters
-                -> IO (Response BSL.ByteString)      -- ^ Response
-doGetRequest url pm = doGetRequestWithReq url pm id
-
--- | TODO: can not be `Request m -> Request m`, why??
---
-doGetRequestWithReq :: String                               -- ^ URL
-                       -> [(BS.ByteString, BS.ByteString)]  -- ^ Extra Parameters
-                       -> (Request (ResourceT IO) -> Request (ResourceT IO))          -- ^ update Request
-                       -> IO (Response BSL.ByteString)      -- ^ Response
-doGetRequestWithReq url pm f = do
-    req <- parseUrl $ url ++ bsToS (renderSimpleQuery True pm)
-    let req' = (updateRequestHeaders .f) req
-    withManager $ httpLbs req'
-
-
--- | Conduct POST request with given URL with post body data.
---
-doPostRequst ::  String                               -- ^ URL
-                 -> [(BS.ByteString, BS.ByteString)]  -- ^ Data to Post Body
-                 -> IO (Response BSL.ByteString)      -- ^ Response
-doPostRequst url body = doPostRequstWithReq url body id
-
-doPostRequstWithReq ::  String                               -- ^ URL
-                        -> [(BS.ByteString, BS.ByteString)]  -- ^ Data to Post Body
-                        -> (Request (ResourceT IO) -> Request (ResourceT IO))
-                        -> IO (Response BSL.ByteString)      -- ^ Response
-doPostRequstWithReq url body f = do
-    req <- parseUrl url
-    let req' = (updateRequestHeaders . f) req
-    withManager $ httpLbs (urlEncodedBody body req')
-
-
---------------------------------------------------
--- Utils
---------------------------------------------------
-
-handleResponse :: Response BSL.ByteString -> IO BSL.ByteString
-handleResponse rsp = if (HT.statusCode . responseStatus) rsp == 200
-                     then return (responseBody rsp)
-                     else throwIO . OAuthException $
-                          "Gaining token failed: " ++ BSL.unpack (responseBody rsp)
-
-updateRequestHeaders :: Request m -> Request m
-updateRequestHeaders req = req { requestHeaders = [ (HT.hAccept, "application/json") ] }
-
-bsToS ::  BS.ByteString -> String
-bsToS = T.unpack . T.decodeUtf8
diff --git a/src/Network/OAuth2.hs b/src/Network/OAuth2.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2.hs
@@ -0,0 +1,26 @@
+-- | A lightweight oauth2 Haskell binding.
+-- See Readme for more details
+module Network.OAuth2 (
+  module Network.OAuth2.Internal,
+
+  -- * Authorization Requset
+  module Network.OAuth2.AuthorizationRequest,
+
+  -- * Token Request
+  module Network.OAuth2.TokenRequest,
+
+  -- * OAuth'ed http client utilities
+  module Network.OAuth2.HttpClient,
+) where
+
+{-
+  Hiding Errors data type from default.
+  Shall qualified import given the naming collision.
+-}
+import Network.OAuth2.AuthorizationRequest hiding (
+  AuthorizationResponseError (..),
+  AuthorizationResponseErrorCode (..),
+ )
+import Network.OAuth2.HttpClient
+import Network.OAuth2.Internal
+import Network.OAuth2.TokenRequest
diff --git a/src/Network/OAuth2/AuthorizationRequest.hs b/src/Network/OAuth2/AuthorizationRequest.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/AuthorizationRequest.hs
@@ -0,0 +1,88 @@
+-- | Bindings Authorization part of The OAuth 2.0 Authorization Framework
+-- RFC6749 <https://www.rfc-editor.org/rfc/rfc6749>
+module Network.OAuth2.AuthorizationRequest where
+
+import Data.Aeson
+import Data.Function (on)
+import Data.List qualified as List
+import Data.Text (Text)
+import Data.Text.Encoding qualified as T
+import Lens.Micro (over)
+import Network.OAuth2.Internal
+import URI.ByteString
+import Prelude hiding (error)
+
+--------------------------------------------------
+
+-- * Authorization Request Errors
+
+--------------------------------------------------
+
+-- | Authorization Code Grant Error Responses https://tools.ietf.org/html/rfc6749#section-4.1.2.1
+--
+-- I found it hard to figure out a way to test the authorization error flow.
+-- When anything goes wrong in an @/authorize@ request, it gets stuck at the provider page,
+-- hence no way for this library to parse error response.
+-- In other words, @/authorize@ ends up with 4xx or 5xx.
+-- Revisit this whenever you find a case where an OAuth2 provider redirects back to the relying party with errors.
+data AuthorizationResponseError = AuthorizationResponseError
+  { authorizationResponseError :: AuthorizationResponseErrorCode
+  , authorizationResponseErrorDescription :: Maybe Text
+  , authorizationResponseErrorUri :: Maybe (URIRef Absolute)
+  }
+  deriving (Show, Eq)
+
+data AuthorizationResponseErrorCode
+  = InvalidRequest
+  | UnauthorizedClient
+  | AccessDenied
+  | UnsupportedResponseType
+  | InvalidScope
+  | ServerError
+  | TemporarilyUnavailable
+  | UnknownErrorCode Text
+  deriving (Show, Eq)
+
+instance FromJSON AuthorizationResponseErrorCode where
+  parseJSON = withText "parseJSON AuthorizationResponseErrorCode" $ \t ->
+    pure $ case t of
+      "invalid_request" -> InvalidRequest
+      "unauthorized_client" -> UnauthorizedClient
+      "access_denied" -> AccessDenied
+      "unsupported_response_type" -> UnsupportedResponseType
+      "invalid_scope" -> InvalidScope
+      "server_error" -> ServerError
+      "temporarily_unavailable" -> TemporarilyUnavailable
+      _ -> UnknownErrorCode t
+
+instance FromJSON AuthorizationResponseError where
+  parseJSON = withObject "parseJSON AuthorizationResponseError" $ \t -> do
+    authorizationResponseError <- t .: "error"
+    authorizationResponseErrorDescription <- t .:? "error_description"
+    authorizationResponseErrorUri <- t .:? "error_uri"
+    pure AuthorizationResponseError {..}
+
+--------------------------------------------------
+
+-- * URLs
+
+--------------------------------------------------
+
+-- | See 'authorizationUrlWithParams'
+authorizationUrl :: OAuth2 -> URI
+authorizationUrl = authorizationUrlWithParams []
+
+-- | Prepare the authorization URL.  Redirect to this URL
+-- asking for user interactive authentication.
+--
+-- @since 2.6.0
+authorizationUrlWithParams :: QueryParams -> OAuth2 -> URI
+authorizationUrlWithParams qs oa = over (queryL . queryPairsL) (++ queryParts) (oauth2AuthorizeEndpoint oa)
+  where
+    queryParts =
+      List.nubBy ((==) `on` fst) $
+        qs
+          ++ [ ("client_id", T.encodeUtf8 $ oauth2ClientId oa)
+             , ("response_type", "code")
+             , ("redirect_uri", serializeURIRef' $ oauth2RedirectUri oa)
+             ]
diff --git a/src/Network/OAuth2/Experiment.hs b/src/Network/OAuth2/Experiment.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment.hs
@@ -0,0 +1,157 @@
+-- | This module contains a new way of doing OAuth2 authorization and authentication
+-- in order to obtain an access token and maybe a refresh token based on RFC 6749.
+--
+-- This module will become the default in a future release.
+--
+-- The key concept is introducing grant flows, which determine the entire workflow per the spec.
+-- Each workflow has slightly different request parameters, which is why you'll often see
+-- different configuration options when creating an OAuth2 application in an IdP developer console.
+--
+-- Here are the supported flows:
+--
+-- 1. Authorization Code. This flow requires an authorize call to obtain an authorization code,
+-- then exchange the code for tokens.
+--
+-- 2. Resource Owner Password. This flow only requires hitting the token endpoint with, of course,
+-- username and password, to obtain tokens.
+--
+-- 3. Client Credentials. This flow also only requires hitting the token endpoint, but with different parameters.
+-- The client credentials flow does not involve an end user, so you won't be able to hit the userinfo endpoint
+-- with the access token you obtain.
+--
+-- 4. PKCE (RFC 7636). This is an enhancement on top of the authorization code flow.
+--
+-- The implicit flow is not supported because it is primarily for SPAs (single-page apps),
+-- and it has been deprecated in favor of the authorization code flow with PKCE.
+--
+-- Here is a quick sample showing how to use the vocabulary from this module.
+--
+-- First, initialize your IdP (using Google as an example) and the application.
+--
+-- @
+--
+-- import Network.OAuth2.Experiment
+-- import URI.ByteString.QQ
+--
+-- data Google = Google deriving (Eq, Show)
+--
+-- googleIdp :: Idp Google
+-- googleIdp =
+--   Idp
+--     { idpAuthorizeEndpoint = [uri|https:\/\/accounts.google.com\/o\/oauth2\/v2\/auth|]
+--     , idpTokenEndpoint = [uri|https:\/\/oauth2.googleapis.com\/token|]
+--     , idpUserInfoEndpoint = [uri|https:\/\/www.googleapis.com\/oauth2\/v2\/userinfo|]
+--     , idpDeviceAuthorizationEndpoint = Just [uri|https:\/\/oauth2.googleapis.com\/device\/code|]
+--     }
+--
+-- fooApp :: AuthorizationCodeApplication
+-- fooApp =
+--   AuthorizationCodeApplication
+--     { acClientId = "xxxxx",
+--       acClientSecret = "xxxxx",
+--       acScope =
+--         Set.fromList
+--           [ \"https:\/\/www.googleapis.com\/auth\/userinfo.email\",
+--             \"https:\/\/www.googleapis.com\/auth\/userinfo.profile\"
+--           ],
+--       acAuthorizeState = \"CHANGE_ME\",
+--       acAuthorizeRequestExtraParams = Map.empty,
+--       acRedirectUri = [uri|http:\/\/localhost\/oauth2\/callback|],
+--       acName = "sample-google-authorization-code-app",
+--       acClientAuthenticationMethod = ClientSecretBasic,
+--     }
+--
+-- fooIdpApplication :: IdpApplication AuthorizationCodeApplication Google
+-- fooIdpApplication = IdpApplication fooApp googleIdp
+-- @
+--
+-- Second, construct the authorize URL.
+--
+-- @
+-- authorizeUrl = mkAuthorizationRequest fooIdpApplication
+-- @
+--
+-- Third, after a successful redirect with an authorization code,
+-- you can exchange it for an access token.
+--
+-- @
+-- mgr <- liftIO $ newManager tlsManagerSettings
+-- tokenResp <- conduitTokenRequest fooIdpApplication mgr authorizeCode
+-- @
+--
+-- If you'd like to fetch user info, use this method:
+--
+-- @
+-- conduitUserInfoRequest fooIdpApplication mgr (accessToken tokenResp)
+-- @
+--
+-- You can also find an example in the @hoauth2-providers-tutorial@ module.
+module Network.OAuth2.Experiment (
+  -- * Application per Grant type
+  module Network.OAuth2.Experiment.Grants,
+
+  -- * Authorization Code
+  mkAuthorizationRequest,
+  mkPkceAuthorizeRequest,
+
+  -- * Device Authorization
+  module Network.OAuth2.Experiment.Flows.DeviceAuthorizationRequest,
+  conduitDeviceAuthorizationRequest,
+  pollDeviceTokenRequest,
+
+  -- * Token Request
+  module Network.OAuth2.Experiment.Flows.TokenRequest,
+  conduitPkceTokenRequest,
+  conduitTokenRequest,
+
+  -- * Refresh Token Request
+  module Network.OAuth2.Experiment.Flows.RefreshTokenRequest,
+  conduitRefreshTokenRequest,
+
+  -- * UserInfo Request
+  module Network.OAuth2.Experiment.Flows.UserInfoRequest,
+  conduitUserInfoRequest,
+  conduitUserInfoRequestWithCustomMethod,
+
+  -- * Types
+  module Network.OAuth2.Experiment.Types,
+  module Network.OAuth2.Experiment.Pkce,
+  module Network.OAuth2,
+
+  -- * Utils
+  module Network.OAuth2.Experiment.Utils,
+) where
+
+import Network.OAuth2 (ClientAuthenticationMethod (..))
+import Network.OAuth2.Experiment.Flows
+import Network.OAuth2.Experiment.Flows.DeviceAuthorizationRequest (
+  DeviceAuthorizationResponse (..),
+ )
+import Network.OAuth2.Experiment.Flows.RefreshTokenRequest (
+  HasRefreshTokenRequest,
+ )
+import Network.OAuth2.Experiment.Flows.TokenRequest (
+  ExchangeTokenInfo,
+  HasTokenRequest,
+  NoNeedExchangeToken (..),
+  TokenRequest,
+ )
+import Network.OAuth2.Experiment.Flows.UserInfoRequest (
+  HasUserInfoRequest,
+ )
+import Network.OAuth2.Experiment.Grants
+import Network.OAuth2.Experiment.Pkce (
+  CodeVerifier (..),
+ )
+import Network.OAuth2.Experiment.Types (
+  AuthorizeState (..),
+  ClientId (..),
+  ClientSecret (..),
+  Idp (..),
+  IdpApplication (..),
+  Password (..),
+  RedirectUri (..),
+  Scope (..),
+  Username (..),
+ )
+import Network.OAuth2.Experiment.Utils (uriToText)
diff --git a/src/Network/OAuth2/Experiment/Flows.hs b/src/Network/OAuth2/Experiment/Flows.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Flows.hs
@@ -0,0 +1,273 @@
+{-# LANGUAGE FlexibleContexts #-}
+
+-- | Module implementing various OAuth2 flow types and their request/response handling.
+-- Provides support for:
+--
+--   * Authorization Code Grant
+--   * Device Authorization Grant
+--   * PKCE Extension
+--   * Token Refresh
+--   * User Info Endpoints
+module Network.OAuth2.Experiment.Flows where
+
+import Control.Concurrent
+import Control.Monad.IO.Class (MonadIO (..))
+import Control.Monad.Trans.Except
+import Data.Aeson (FromJSON)
+import Data.Bifunctor
+import Data.ByteString.Lazy.Char8 qualified as BSL
+import Data.Map.Strict qualified as Map
+import Data.Maybe
+import Network.HTTP.Client.Contrib
+import Network.HTTP.Conduit
+import Network.OAuth2
+import Network.OAuth2 qualified as OAuth2
+import Network.OAuth2.Experiment.Flows.DeviceAuthorizationRequest
+import Network.OAuth2.Experiment.Flows.RefreshTokenRequest
+import Network.OAuth2.Experiment.Flows.TokenRequest
+import Network.OAuth2.Experiment.Flows.UserInfoRequest
+import Network.OAuth2.Experiment.Grants.AuthorizationCode
+import Network.OAuth2.Experiment.Grants.DeviceAuthorization
+import Network.OAuth2.Experiment.Pkce
+import Network.OAuth2.Experiment.Types
+import Network.OAuth2.Experiment.Utils
+import URI.ByteString hiding (UserInfo)
+
+-------------------------------------------------------------------------------
+--                           Authorization Requests                          --
+-------------------------------------------------------------------------------
+
+-- | Constructs an Authorization Code request URI according to
+-- <https://www.rfc-editor.org/rfc/rfc6749#section-4.1.1 RFC 6749 Section 4.1.1>.
+--
+-- The generated URI includes:
+--   * client_id
+--   * response_type (always "code")
+--   * redirect_uri
+--   * state (if provided)
+--   * scope (if provided)
+mkAuthorizationRequest :: IdpApplication i AuthorizationCodeApplication -> URI
+mkAuthorizationRequest idpApp =
+  let req = mkAuthorizationRequestParam (application idpApp)
+      allParams =
+        map (bimap tlToBS tlToBS) $
+          Map.toList $
+            toQueryParam req
+   in appendQueryParams allParams $
+        idpAuthorizeEndpoint (idp idpApp)
+
+-- | Constructs an Authorization Code request URI with PKCE support according to
+-- <https://datatracker.ietf.org/doc/html/rfc7636 RFC 7636>.
+--
+-- Returns both the authorization URI and the generated code verifier.
+-- The code verifier must be stored securely for later use in the token request.
+mkPkceAuthorizeRequest ::
+  MonadIO m =>
+  IdpApplication i AuthorizationCodeApplication ->
+  m (URI, CodeVerifier)
+mkPkceAuthorizeRequest IdpApplication {..} = do
+  (req, codeVerifier) <- mkPkceAuthorizeRequestParam application
+  let allParams = map (bimap tlToBS tlToBS) $ Map.toList $ toQueryParam req
+  let url =
+        appendQueryParams allParams $
+          idpAuthorizeEndpoint idp
+  pure (url, codeVerifier)
+
+-------------------------------------------------------------------------------
+--                                Device Auth                                --
+-------------------------------------------------------------------------------
+
+-- | Makes Device Authorization Request
+-- https://www.rfc-editor.org/rfc/rfc8628#section-3.1
+conduitDeviceAuthorizationRequest ::
+  MonadIO m =>
+  IdpApplication i DeviceAuthorizationApplication ->
+  Manager ->
+  ExceptT BSL.ByteString m DeviceAuthorizationResponse
+conduitDeviceAuthorizationRequest IdpApplication {..} mgr = do
+  case idpDeviceAuthorizationEndpoint idp of
+    Nothing -> throwE "[conduitDeviceAuthorizationRequest] Device Authorization Flow is not supported: missing device_authorization_endpoint."
+    Just deviceAuthEndpoint -> do
+      let deviceAuthReq = mkDeviceAuthorizationRequestParam application
+          body = unionMapsToQueryParams [toQueryParam deviceAuthReq]
+      ExceptT . liftIO $ do
+        req <- addDefaultRequestHeaders <$> uriToRequest deviceAuthEndpoint
+        let req' =
+              if daAuthorizationRequestAuthenticationMethod application == ClientSecretBasic
+                then addSecretToHeader (daClientId application) (daClientSecret application) req
+                else req
+        resp <- httpLbs (urlEncodedBody body req') mgr
+        pure $ first ("[conduitDeviceAuthorizationRequest] " <>) $ handleResponseJSON resp
+
+-- | Polls for a token using the device authorization flow.
+--
+-- This implements the polling mechanism described in
+-- <https://www.rfc-editor.org/rfc/rfc8628#section-3.5 RFC 8628 Section 3.5>.
+-- Handles automatic retries and interval adjustments based on IdP responses.
+pollDeviceTokenRequest ::
+  MonadIO m =>
+  IdpApplication i DeviceAuthorizationApplication ->
+  Manager ->
+  DeviceAuthorizationResponse ->
+  ExceptT TokenResponseError m TokenResponse
+pollDeviceTokenRequest idpApp mgr deviceAuthResp = do
+  pollDeviceTokenRequestInternal
+    idpApp
+    mgr
+    (deviceCode deviceAuthResp)
+    (fromMaybe 5 $ interval deviceAuthResp)
+
+pollDeviceTokenRequestInternal ::
+  MonadIO m =>
+  IdpApplication i DeviceAuthorizationApplication ->
+  Manager ->
+  DeviceCode ->
+  Int ->
+  -- | Polling Interval
+  ExceptT TokenResponseError m TokenResponse
+pollDeviceTokenRequestInternal idpApp mgr deviceCode intervalSeconds = do
+  resp <- runExceptT (conduitTokenRequest idpApp mgr deviceCode)
+  case resp of
+    Left trRespError -> do
+      case tokenResponseError trRespError of
+        -- TODO: Didn't have a good idea to expand the error code
+        -- specifically for device token request flow
+        -- Device Token Response additional error code: https://www.rfc-editor.org/rfc/rfc8628#section-3.5
+        UnknownErrorCode "authorization_pending" -> do
+          liftIO $ threadDelay $ intervalSeconds * 1000000
+          pollDeviceTokenRequestInternal idpApp mgr deviceCode intervalSeconds
+        UnknownErrorCode "slow_down" -> do
+          let newIntervalSeconds = intervalSeconds + 5
+          liftIO $ threadDelay $ newIntervalSeconds * 1000000
+          pollDeviceTokenRequestInternal idpApp mgr deviceCode newIntervalSeconds
+        _ -> throwE trRespError
+    Right v -> pure v
+
+-------------------------------------------------------------------------------
+--                               Token Request                               --
+-------------------------------------------------------------------------------
+
+-- | Sends a token request according to
+-- <https://www.rfc-editor.org/rfc/rfc6749#section-4.1.3 RFC 6749 Section 4.1.3>.
+--
+-- This is used for exchanging authorization codes, device codes, or other
+-- grant types for access tokens.
+conduitTokenRequest ::
+  (HasTokenRequest a, ToQueryParam (TokenRequest a), MonadIO m) =>
+  IdpApplication i a ->
+  Manager ->
+  ExchangeTokenInfo a ->
+  ExceptT TokenResponseError m TokenResponse
+conduitTokenRequest idpApp mgr exchangeToken = do
+  let req = mkTokenRequestParam (application idpApp) exchangeToken
+      body =
+        unionMapsToQueryParams
+          [ toQueryParam req
+          ]
+   in conduitTokenRequestInternal idpApp mgr body
+
+-------------------------------------------------------------------------------
+--                             PKCE Token Request                            --
+-------------------------------------------------------------------------------
+
+-- | https://datatracker.ietf.org/doc/html/rfc7636#section-4.5
+conduitPkceTokenRequest ::
+  (HasTokenRequest a, ToQueryParam (TokenRequest a), MonadIO m) =>
+  IdpApplication i a ->
+  Manager ->
+  (ExchangeTokenInfo a, CodeVerifier) ->
+  ExceptT TokenResponseError m TokenResponse
+conduitPkceTokenRequest idpApp mgr (exchangeToken, codeVerifier) =
+  let req = mkTokenRequestParam (application idpApp) exchangeToken
+      body =
+        unionMapsToQueryParams
+          [ toQueryParam req
+          , toQueryParam codeVerifier
+          ]
+   in conduitTokenRequestInternal idpApp mgr body
+
+-------------------------------------------------------------------------------
+--                              Refresh Token                               --
+-------------------------------------------------------------------------------
+
+-- | Makes a Refresh Token Request according to
+-- <https://www.rfc-editor.org/rfc/rfc6749#section-6 RFC 6749 Section 6>.
+--
+-- Used to obtain a new access token using a refresh token.
+conduitRefreshTokenRequest ::
+  (MonadIO m, HasRefreshTokenRequest a) =>
+  IdpApplication i a ->
+  Manager ->
+  OAuth2.RefreshToken ->
+  ExceptT TokenResponseError m TokenResponse
+conduitRefreshTokenRequest ia mgr rt =
+  let tokenReq = mkRefreshTokenRequestParam (application ia) rt
+      body = unionMapsToQueryParams [toQueryParam tokenReq]
+   in conduitTokenRequestInternal ia mgr body
+
+-------------------------------------------------------------------------------
+--                                 User Info                                 --
+-------------------------------------------------------------------------------
+
+-- | Makes a standard request to the userinfo endpoint using GET method.
+--
+-- This is commonly used with OpenID Connect providers to fetch
+-- user profile information using an access token.
+conduitUserInfoRequest ::
+  (MonadIO m, HasUserInfoRequest a, FromJSON b) =>
+  IdpApplication i a ->
+  Manager ->
+  AccessToken ->
+  ExceptT BSL.ByteString m b
+conduitUserInfoRequest = conduitUserInfoRequestWithCustomMethod authGetJSON
+
+-- | Makes a request to the userinfo endpoint using a custom HTTP method.
+--
+-- Some IdPs may require different HTTP methods (instead of GET) or custom headers
+-- for fetching user information. This function provides that flexibility.
+conduitUserInfoRequestWithCustomMethod ::
+  (MonadIO m, HasUserInfoRequest a, FromJSON b) =>
+  ( Manager ->
+    AccessToken ->
+    URI ->
+    ExceptT BSL.ByteString m b
+  ) ->
+  IdpApplication i a ->
+  Manager ->
+  AccessToken ->
+  ExceptT BSL.ByteString m b
+conduitUserInfoRequestWithCustomMethod fetchMethod IdpApplication {..} mgr at =
+  fetchMethod mgr at (idpUserInfoEndpoint idp)
+
+-------------------------------------------------------------------------------
+--                              Internal helpers                             --
+-------------------------------------------------------------------------------
+
+conduitTokenRequestInternal ::
+  ( MonadIO m
+  , HasClientAuthenticationMethod a
+  , FromJSON b
+  ) =>
+  IdpApplication i a ->
+  -- | HTTP connection manager.
+  Manager ->
+  -- | Request body.
+  PostBody ->
+  -- | Response as ByteString
+  ExceptT TokenResponseError m b
+conduitTokenRequestInternal IdpApplication {..} manager body = do
+  let clientAuthMethod = getClientAuthenticationMethod application
+      url = idpTokenEndpoint idp
+      updateAuthHeader =
+        case clientAuthMethod of
+          ClientSecretBasic -> addClientAuthToHeader application
+          ClientSecretPost -> id
+          ClientAssertionJwt -> id
+      go = do
+        req <- uriToRequest url
+        let req' = (updateAuthHeader . addDefaultRequestHeaders) req
+        httpLbs (urlEncodedBody body req') manager
+  resp <- ExceptT . liftIO $ fmap handleOAuth2TokenResponse go
+  case parseResponseFlexible resp of
+    Right obj -> return obj
+    Left e -> throwE e
diff --git a/src/Network/OAuth2/Experiment/Flows/AuthorizationRequest.hs b/src/Network/OAuth2/Experiment/Flows/AuthorizationRequest.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Flows/AuthorizationRequest.hs
@@ -0,0 +1,33 @@
+module Network.OAuth2.Experiment.Flows.AuthorizationRequest where
+
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Set (Set)
+import Data.Text.Lazy (Text)
+import Network.OAuth2.Experiment.Types
+
+-------------------------------------------------------------------------------
+--                           Authorization Request                           --
+-------------------------------------------------------------------------------
+
+data AuthorizationRequestParam = AuthorizationRequestParam
+  { arScope :: Set Scope
+  , arState :: AuthorizeState
+  , arClientId :: ClientId
+  , arRedirectUri :: Maybe RedirectUri
+  , arResponseType :: ResponseType
+  -- ^ It could be optional there is only one redirect_uri registered.
+  -- See: https://www.rfc-editor.org/rfc/rfc6749#section-3.1.2.3
+  , arExtraParams :: Map Text Text
+  }
+
+instance ToQueryParam AuthorizationRequestParam where
+  toQueryParam AuthorizationRequestParam {..} =
+    Map.unions
+      [ toQueryParam arResponseType
+      , toQueryParam arScope
+      , toQueryParam arClientId
+      , toQueryParam arState
+      , toQueryParam arRedirectUri
+      , arExtraParams
+      ]
diff --git a/src/Network/OAuth2/Experiment/Flows/DeviceAuthorizationRequest.hs b/src/Network/OAuth2/Experiment/Flows/DeviceAuthorizationRequest.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Flows/DeviceAuthorizationRequest.hs
@@ -0,0 +1,59 @@
+{-# LANGUAGE DerivingStrategies #-}
+
+module Network.OAuth2.Experiment.Flows.DeviceAuthorizationRequest where
+
+import Control.Applicative
+import Data.Aeson.Types
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Set (Set)
+import Data.Text.Lazy (Text)
+import Network.OAuth2.Experiment.Types
+import URI.ByteString hiding (UserInfo)
+
+-------------------------------------------------------------------------------
+--                    Device Authorization Request                           --
+-------------------------------------------------------------------------------
+newtype DeviceCode = DeviceCode Text
+  deriving newtype (FromJSON)
+
+instance ToQueryParam DeviceCode where
+  toQueryParam :: DeviceCode -> Map Text Text
+  toQueryParam (DeviceCode dc) = Map.singleton "device_code" dc
+
+-- | https://www.rfc-editor.org/rfc/rfc8628#section-3.2
+data DeviceAuthorizationResponse = DeviceAuthorizationResponse
+  { deviceCode :: DeviceCode
+  , userCode :: Text
+  , verificationUri :: URI
+  , verificationUriComplete :: Maybe URI
+  , expiresIn :: Integer
+  , interval :: Maybe Int
+  }
+
+instance FromJSON DeviceAuthorizationResponse where
+  parseJSON :: Value -> Parser DeviceAuthorizationResponse
+  parseJSON = withObject "parse DeviceAuthorizationResponse" $ \t -> do
+    deviceCode <- t .: "device_code"
+    userCode <- t .: "user_code"
+    -- https://stackoverflow.com/questions/76696956/shall-it-be-verification-uri-instead-of-verification-url-in-the-device-autho
+    verificationUri <- t .: "verification_uri" <|> t .: "verification_url"
+    verificationUriComplete <- t .:? "verification_uri_complete"
+    expiresIn <- t .: "expires_in"
+    interval <- t .:? "interval"
+    pure DeviceAuthorizationResponse {..}
+
+data DeviceAuthorizationRequestParam = DeviceAuthorizationRequestParam
+  { darScope :: Set Scope
+  , darClientId :: Maybe ClientId
+  , darExtraParams :: Map Text Text
+  }
+
+instance ToQueryParam DeviceAuthorizationRequestParam where
+  toQueryParam :: DeviceAuthorizationRequestParam -> Map Text Text
+  toQueryParam DeviceAuthorizationRequestParam {..} =
+    Map.unions
+      [ toQueryParam darScope
+      , toQueryParam darClientId
+      , darExtraParams
+      ]
diff --git a/src/Network/OAuth2/Experiment/Flows/RefreshTokenRequest.hs b/src/Network/OAuth2/Experiment/Flows/RefreshTokenRequest.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Flows/RefreshTokenRequest.hs
@@ -0,0 +1,39 @@
+{-# LANGUAGE FlexibleContexts #-}
+
+module Network.OAuth2.Experiment.Flows.RefreshTokenRequest where
+
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Set (Set)
+import Data.Text.Lazy (Text)
+import Network.OAuth2 qualified as OAuth2
+import Network.OAuth2.Experiment.Flows.TokenRequest
+import Network.OAuth2.Experiment.Types
+
+-------------------------------------------------------------------------------
+--                            RefreshToken Requset                           --
+-------------------------------------------------------------------------------
+
+data RefreshTokenRequest = RefreshTokenRequest
+  { rrRefreshToken :: OAuth2.RefreshToken
+  , rrGrantType :: GrantTypeValue
+  , rrScope :: Set Scope
+  , rrClientId :: Maybe ClientId
+  , rrClientSecret :: Maybe ClientSecret
+  }
+
+instance ToQueryParam RefreshTokenRequest where
+  toQueryParam :: RefreshTokenRequest -> Map Text Text
+  toQueryParam RefreshTokenRequest {..} =
+    Map.unions
+      [ toQueryParam rrGrantType
+      , toQueryParam rrScope
+      , toQueryParam rrRefreshToken
+      , toQueryParam rrClientId
+      , toQueryParam rrClientSecret
+      ]
+
+class HasClientAuthenticationMethod a => HasRefreshTokenRequest a where
+  -- | Make Refresh Token Request parameters
+  -- | https://www.rfc-editor.org/rfc/rfc6749#section-6
+  mkRefreshTokenRequestParam :: a -> OAuth2.RefreshToken -> RefreshTokenRequest
diff --git a/src/Network/OAuth2/Experiment/Flows/TokenRequest.hs b/src/Network/OAuth2/Experiment/Flows/TokenRequest.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Flows/TokenRequest.hs
@@ -0,0 +1,41 @@
+{-# LANGUAGE FlexibleContexts #-}
+
+module Network.OAuth2.Experiment.Flows.TokenRequest where
+
+import Data.Text.Encoding qualified as T
+import Data.Text.Lazy qualified as TL
+import Network.HTTP.Conduit
+import Network.OAuth2 (
+  ClientAuthenticationMethod (..),
+ )
+import Network.OAuth2.Experiment.Types (
+  ClientId (unClientId),
+  ClientSecret (unClientSecret),
+ )
+
+addSecretToHeader :: ClientId -> ClientSecret -> Request -> Request
+addSecretToHeader cid csecret =
+  applyBasicAuth
+    (T.encodeUtf8 $ TL.toStrict $ unClientId cid)
+    (T.encodeUtf8 $ TL.toStrict $ unClientSecret csecret)
+
+class HasClientAuthenticationMethod a where
+  getClientAuthenticationMethod :: a -> ClientAuthenticationMethod
+  addClientAuthToHeader :: a -> Request -> Request
+  addClientAuthToHeader _ = id
+
+-- | Only Authorization Code Grant involves a Exchange Token (Authorization Code).
+-- ResourceOwnerPassword and Client Credentials make token request directly.
+data NoNeedExchangeToken = NoNeedExchangeToken
+
+class HasClientAuthenticationMethod a => HasTokenRequest a where
+  -- Each GrantTypeFlow has slightly different request parameter to /token endpoint.
+  data TokenRequest a
+  type ExchangeTokenInfo a
+
+  -- | Only 'AuthorizationCode flow (but not resource owner password nor client credentials) will use 'ExchangeToken' in the token request
+  -- create type family to be explicit on it.
+  -- with 'type instance WithExchangeToken a b = b' implies no exchange token
+  -- v.s. 'type instance WithExchangeToken a b = ExchangeToken -> b' implies needing an exchange token
+  -- type WithExchangeToken a b
+  mkTokenRequestParam :: a -> ExchangeTokenInfo a -> TokenRequest a
diff --git a/src/Network/OAuth2/Experiment/Flows/UserInfoRequest.hs b/src/Network/OAuth2/Experiment/Flows/UserInfoRequest.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Flows/UserInfoRequest.hs
@@ -0,0 +1,7 @@
+module Network.OAuth2.Experiment.Flows.UserInfoRequest where
+
+-------------------------------------------------------------------------------
+--                             User Info Request                             --
+-------------------------------------------------------------------------------
+
+class HasUserInfoRequest a
diff --git a/src/Network/OAuth2/Experiment/Grants.hs b/src/Network/OAuth2/Experiment/Grants.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Grants.hs
@@ -0,0 +1,15 @@
+module Network.OAuth2.Experiment.Grants (
+  module Network.OAuth2.Experiment.Grants.AuthorizationCode,
+  module Network.OAuth2.Experiment.Grants.DeviceAuthorization,
+  module Network.OAuth2.Experiment.Grants.ClientCredentials,
+  module Network.OAuth2.Experiment.Grants.ResourceOwnerPassword,
+  module Network.OAuth2.Experiment.Grants.JwtBearer,
+) where
+
+import Network.OAuth2.Experiment.Grants.AuthorizationCode (AuthorizationCodeApplication (..))
+import Network.OAuth2.Experiment.Grants.ClientCredentials (ClientCredentialsApplication (..))
+import Network.OAuth2.Experiment.Grants.DeviceAuthorization (
+  DeviceAuthorizationApplication (..),
+ )
+import Network.OAuth2.Experiment.Grants.JwtBearer (JwtBearerApplication (..))
+import Network.OAuth2.Experiment.Grants.ResourceOwnerPassword (ResourceOwnerPasswordApplication (..))
diff --git a/src/Network/OAuth2/Experiment/Grants/AuthorizationCode.hs b/src/Network/OAuth2/Experiment/Grants/AuthorizationCode.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Grants/AuthorizationCode.hs
@@ -0,0 +1,117 @@
+{-# LANGUAGE FlexibleInstances #-}
+
+module Network.OAuth2.Experiment.Grants.AuthorizationCode where
+
+import Control.Monad.IO.Class (MonadIO (..))
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Set (Set)
+import Data.Text.Lazy (Text)
+import Network.OAuth2 (ClientAuthenticationMethod (..), ExchangeToken (..))
+import Network.OAuth2 qualified as OAuth2
+import Network.OAuth2.Experiment.Flows.AuthorizationRequest
+import Network.OAuth2.Experiment.Flows.RefreshTokenRequest
+import Network.OAuth2.Experiment.Flows.TokenRequest
+import Network.OAuth2.Experiment.Flows.UserInfoRequest
+import Network.OAuth2.Experiment.Pkce
+import Network.OAuth2.Experiment.Types
+import Network.OAuth2.Experiment.Utils
+import URI.ByteString hiding (UserInfo)
+
+-- | An Application that supports "Authorization code" flow
+--
+-- https://www.rfc-editor.org/rfc/rfc6749#section-4.1
+data AuthorizationCodeApplication = AuthorizationCodeApplication
+  { acName :: Text
+  , acClientId :: ClientId
+  , acClientSecret :: ClientSecret
+  , acScope :: Set Scope
+  , acRedirectUri :: URI
+  , acAuthorizeState :: AuthorizeState
+  , acAuthorizeRequestExtraParams :: Map Text Text
+  , acClientAuthenticationMethod :: ClientAuthenticationMethod
+  }
+
+instance HasClientAuthenticationMethod AuthorizationCodeApplication where
+  getClientAuthenticationMethod :: AuthorizationCodeApplication -> ClientAuthenticationMethod
+  getClientAuthenticationMethod AuthorizationCodeApplication {..} = acClientAuthenticationMethod
+  addClientAuthToHeader AuthorizationCodeApplication {..} = addSecretToHeader acClientId acClientSecret
+
+mkAuthorizationRequestParam :: AuthorizationCodeApplication -> AuthorizationRequestParam
+mkAuthorizationRequestParam AuthorizationCodeApplication {..} =
+  AuthorizationRequestParam
+    { arScope = acScope
+    , arState = acAuthorizeState
+    , arClientId = acClientId
+    , arRedirectUri = Just (RedirectUri acRedirectUri)
+    , arResponseType = Code
+    , arExtraParams = acAuthorizeRequestExtraParams
+    }
+
+mkPkceAuthorizeRequestParam :: MonadIO m => AuthorizationCodeApplication -> m (AuthorizationRequestParam, CodeVerifier)
+mkPkceAuthorizeRequestParam app = do
+  PkceRequestParam {..} <- mkPkceParam
+  let authReqParam = mkAuthorizationRequestParam app
+      combinatedExtraParams =
+        Map.unions
+          [ arExtraParams authReqParam
+          , toQueryParam codeChallenge
+          , toQueryParam codeChallengeMethod
+          ]
+  pure (authReqParam {arExtraParams = combinatedExtraParams}, codeVerifier)
+
+-- | https://www.rfc-editor.org/rfc/rfc6749#section-4.1.3
+instance HasTokenRequest AuthorizationCodeApplication where
+  type ExchangeTokenInfo AuthorizationCodeApplication = ExchangeToken
+  data TokenRequest AuthorizationCodeApplication = AuthorizationCodeTokenRequest
+    { trCode :: ExchangeToken
+    , trGrantType :: GrantTypeValue
+    , trRedirectUri :: RedirectUri
+    , trClientId :: ClientId
+    , trClientSecret :: ClientSecret
+    , trClientAuthenticationMethod :: ClientAuthenticationMethod
+    }
+
+  mkTokenRequestParam :: AuthorizationCodeApplication -> ExchangeToken -> TokenRequest AuthorizationCodeApplication
+  mkTokenRequestParam AuthorizationCodeApplication {..} authCode =
+    AuthorizationCodeTokenRequest
+      { trCode = authCode
+      , trGrantType = GTAuthorizationCode
+      , trRedirectUri = RedirectUri acRedirectUri
+      , trClientId = acClientId
+      , trClientSecret = acClientSecret
+      , trClientAuthenticationMethod = acClientAuthenticationMethod
+      }
+
+instance ToQueryParam (TokenRequest AuthorizationCodeApplication) where
+  toQueryParam :: TokenRequest AuthorizationCodeApplication -> Map Text Text
+  toQueryParam AuthorizationCodeTokenRequest {..} =
+    let extraBodyBasedOnClientAuthMethod =
+          case trClientAuthenticationMethod of
+            ClientAssertionJwt ->
+              [ Map.fromList
+                  [ ("client_assertion_type", "urn:ietf:params:oauth:client-assertion-type:jwt-bearer")
+                  , ("client_assertion", bs8ToLazyText $ tlToBS $ unClientSecret trClientSecret)
+                  ]
+              ]
+            ClientSecretPost -> [toQueryParam trClientId, toQueryParam trClientSecret]
+            ClientSecretBasic -> []
+     in Map.unions $
+          [ toQueryParam trCode
+          , toQueryParam trGrantType
+          , toQueryParam trRedirectUri
+          ]
+            ++ extraBodyBasedOnClientAuthMethod
+
+instance HasUserInfoRequest AuthorizationCodeApplication
+
+instance HasRefreshTokenRequest AuthorizationCodeApplication where
+  mkRefreshTokenRequestParam :: AuthorizationCodeApplication -> OAuth2.RefreshToken -> RefreshTokenRequest
+  mkRefreshTokenRequestParam AuthorizationCodeApplication {..} rt =
+    RefreshTokenRequest
+      { rrScope = acScope
+      , rrGrantType = GTRefreshToken
+      , rrRefreshToken = rt
+      , rrClientId = if acClientAuthenticationMethod == ClientSecretPost then Just acClientId else Nothing
+      , rrClientSecret = if acClientAuthenticationMethod == ClientSecretPost then Just acClientSecret else Nothing
+      }
diff --git a/src/Network/OAuth2/Experiment/Grants/ClientCredentials.hs b/src/Network/OAuth2/Experiment/Grants/ClientCredentials.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Grants/ClientCredentials.hs
@@ -0,0 +1,73 @@
+{-# LANGUAGE FlexibleInstances #-}
+
+module Network.OAuth2.Experiment.Grants.ClientCredentials where
+
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Set (Set)
+import Data.Text.Lazy (Text)
+import Network.OAuth2 (ClientAuthenticationMethod (..))
+import Network.OAuth2.Experiment.Flows.TokenRequest
+import Network.OAuth2.Experiment.Types
+import Network.OAuth2.Experiment.Utils
+
+-- | An Application that supports "Client Credentials" flow
+--
+-- https://www.rfc-editor.org/rfc/rfc6749#section-4.4
+data ClientCredentialsApplication = ClientCredentialsApplication
+  { ccClientId :: ClientId
+  , ccClientSecret :: ClientSecret
+  , ccName :: Text
+  , ccScope :: Set Scope
+  , ccTokenRequestExtraParams :: Map Text Text
+  , ccClientAuthenticationMethod :: ClientAuthenticationMethod
+  }
+
+instance HasClientAuthenticationMethod ClientCredentialsApplication where
+  getClientAuthenticationMethod :: ClientCredentialsApplication -> ClientAuthenticationMethod
+  getClientAuthenticationMethod ClientCredentialsApplication {..} = ccClientAuthenticationMethod
+
+  addClientAuthToHeader ClientCredentialsApplication {..} = addSecretToHeader ccClientId ccClientSecret
+
+-- | https://www.rfc-editor.org/rfc/rfc6749#section-4.4.2
+instance HasTokenRequest ClientCredentialsApplication where
+  type ExchangeTokenInfo ClientCredentialsApplication = NoNeedExchangeToken
+  data TokenRequest ClientCredentialsApplication = ClientCredentialsTokenRequest
+    { trScope :: Set Scope
+    , trGrantType :: GrantTypeValue
+    , trClientSecret :: ClientSecret
+    , trClientId :: ClientId
+    , trExtraParams :: Map Text Text
+    , trClientAuthenticationMethod :: ClientAuthenticationMethod
+    }
+
+  mkTokenRequestParam :: ClientCredentialsApplication -> NoNeedExchangeToken -> TokenRequest ClientCredentialsApplication
+  mkTokenRequestParam ClientCredentialsApplication {..} _ =
+    ClientCredentialsTokenRequest
+      { trScope = ccScope
+      , trGrantType = GTClientCredentials
+      , trClientSecret = ccClientSecret
+      , trClientAuthenticationMethod = ccClientAuthenticationMethod
+      , trExtraParams = ccTokenRequestExtraParams
+      , trClientId = ccClientId
+      }
+
+instance ToQueryParam (TokenRequest ClientCredentialsApplication) where
+  toQueryParam :: TokenRequest ClientCredentialsApplication -> Map Text Text
+  toQueryParam ClientCredentialsTokenRequest {..} =
+    let extraBodyBasedOnClientAuthMethod =
+          case trClientAuthenticationMethod of
+            ClientAssertionJwt ->
+              [ Map.fromList
+                  [ ("client_assertion_type", "urn:ietf:params:oauth:client-assertion-type:jwt-bearer")
+                  , ("client_assertion", bs8ToLazyText $ tlToBS $ unClientSecret trClientSecret)
+                  ]
+              ]
+            ClientSecretPost -> [toQueryParam trClientId, toQueryParam trClientSecret]
+            ClientSecretBasic -> []
+     in Map.unions $
+          [ toQueryParam trGrantType
+          , toQueryParam trScope
+          , trExtraParams
+          ]
+            ++ extraBodyBasedOnClientAuthMethod
diff --git a/src/Network/OAuth2/Experiment/Grants/DeviceAuthorization.hs b/src/Network/OAuth2/Experiment/Grants/DeviceAuthorization.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Grants/DeviceAuthorization.hs
@@ -0,0 +1,90 @@
+{-# LANGUAGE FlexibleInstances #-}
+
+module Network.OAuth2.Experiment.Grants.DeviceAuthorization where
+
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Maybe
+import Data.Set (Set)
+import Data.Text.Lazy (Text)
+import Network.OAuth2
+import Network.OAuth2.Experiment.Flows.DeviceAuthorizationRequest
+import Network.OAuth2.Experiment.Flows.TokenRequest
+import Network.OAuth2.Experiment.Flows.UserInfoRequest
+import Network.OAuth2.Experiment.Types
+import Prelude hiding (error)
+
+-- | An Application that supports "Device Authorization Grant"
+--
+-- https://www.rfc-editor.org/rfc/rfc8628#section-3.1
+data DeviceAuthorizationApplication = DeviceAuthorizationApplication
+  { daName :: Text
+  , daClientId :: ClientId
+  , daClientSecret :: ClientSecret
+  , daScope :: Set Scope
+  , daAuthorizationRequestExtraParam :: Map Text Text
+  -- ^ Additional parameters to the device authorization request.
+  -- Most of identity providers follow the spec strictly but
+  -- AzureAD requires "tenant" parameter.
+  , daAuthorizationRequestAuthenticationMethod :: ClientAuthenticationMethod
+  -- ^ The spec requires similar authentication method as /token request.
+  -- Most of identity providers doesn't required it but some does like Okta.
+  }
+
+instance HasClientAuthenticationMethod DeviceAuthorizationApplication where
+  getClientAuthenticationMethod :: DeviceAuthorizationApplication -> ClientAuthenticationMethod
+  getClientAuthenticationMethod = daAuthorizationRequestAuthenticationMethod
+  addClientAuthToHeader DeviceAuthorizationApplication {..} = addSecretToHeader daClientId daClientSecret
+
+mkDeviceAuthorizationRequestParam :: DeviceAuthorizationApplication -> DeviceAuthorizationRequestParam
+mkDeviceAuthorizationRequestParam DeviceAuthorizationApplication {..} =
+  DeviceAuthorizationRequestParam
+    { darScope = daScope
+    , darClientId =
+        if daAuthorizationRequestAuthenticationMethod == ClientSecretPost
+          then Just daClientId
+          else Nothing
+    , darExtraParams = daAuthorizationRequestExtraParam
+    }
+
+-- | https://www.rfc-editor.org/rfc/rfc8628#section-3.4
+instance HasTokenRequest DeviceAuthorizationApplication where
+  type ExchangeTokenInfo DeviceAuthorizationApplication = DeviceCode
+  data TokenRequest DeviceAuthorizationApplication = AuthorizationCodeTokenRequest
+    { trCode :: DeviceCode
+    , trGrantType :: GrantTypeValue
+    , trClientId :: Maybe ClientId
+    }
+
+  mkTokenRequestParam ::
+    DeviceAuthorizationApplication ->
+    DeviceCode ->
+    TokenRequest DeviceAuthorizationApplication
+  mkTokenRequestParam DeviceAuthorizationApplication {..} deviceCode =
+    --
+    -- This is a bit hacky!
+    -- The token request use `ClientSecretBasic` by default. (has to pick up one Client Authn Method)
+    -- ClientId shall be also be in request body per spec.
+    -- However, for some IdPs, e.g. Okta, when using `ClientSecretBasic` to authn Client,
+    -- it doesn't allow @client_id@ in the request body
+    -- 'daAuthorizationRequestAuthenticationMethod' set the tone for Authorization Request,
+    -- hence just follow it in the token request
+    AuthorizationCodeTokenRequest
+      { trCode = deviceCode
+      , trGrantType = GTDeviceCode
+      , trClientId =
+          if daAuthorizationRequestAuthenticationMethod == ClientSecretPost
+            then Just daClientId
+            else Nothing
+      }
+
+instance ToQueryParam (TokenRequest DeviceAuthorizationApplication) where
+  toQueryParam :: TokenRequest DeviceAuthorizationApplication -> Map Text Text
+  toQueryParam AuthorizationCodeTokenRequest {..} =
+    Map.unions
+      [ toQueryParam trCode
+      , toQueryParam trGrantType
+      , toQueryParam trClientId
+      ]
+
+instance HasUserInfoRequest DeviceAuthorizationApplication
diff --git a/src/Network/OAuth2/Experiment/Grants/JwtBearer.hs b/src/Network/OAuth2/Experiment/Grants/JwtBearer.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Grants/JwtBearer.hs
@@ -0,0 +1,50 @@
+{-# LANGUAGE FlexibleInstances #-}
+
+module Network.OAuth2.Experiment.Grants.JwtBearer where
+
+import Data.ByteString qualified as BS
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Text.Lazy (Text)
+import Network.OAuth2 (ClientAuthenticationMethod (..))
+import Network.OAuth2.Experiment.Flows.TokenRequest
+import Network.OAuth2.Experiment.Flows.UserInfoRequest
+import Network.OAuth2.Experiment.Types
+import Network.OAuth2.Experiment.Utils
+
+-- | An Application that supports "JWT Bearer" flow
+--
+-- https://datatracker.ietf.org/doc/html/rfc7523
+data JwtBearerApplication = JwtBearerApplication
+  { jbName :: Text
+  , jbJwtAssertion :: BS.ByteString
+  }
+
+instance HasClientAuthenticationMethod JwtBearerApplication where
+  getClientAuthenticationMethod :: JwtBearerApplication -> ClientAuthenticationMethod
+  getClientAuthenticationMethod _ = ClientAssertionJwt
+
+instance HasTokenRequest JwtBearerApplication where
+  type ExchangeTokenInfo JwtBearerApplication = NoNeedExchangeToken
+
+  data TokenRequest JwtBearerApplication = JwtBearerTokenRequest
+    { trGrantType :: GrantTypeValue -- \| 'GTJwtBearer'
+    , trAssertion :: BS.ByteString -- \| The the signed JWT token
+    }
+
+  mkTokenRequestParam :: JwtBearerApplication -> NoNeedExchangeToken -> TokenRequest JwtBearerApplication
+  mkTokenRequestParam JwtBearerApplication {..} _ =
+    JwtBearerTokenRequest
+      { trGrantType = GTJwtBearer
+      , trAssertion = jbJwtAssertion
+      }
+
+instance ToQueryParam (TokenRequest JwtBearerApplication) where
+  toQueryParam :: TokenRequest JwtBearerApplication -> Map Text Text
+  toQueryParam JwtBearerTokenRequest {..} =
+    Map.unions
+      [ toQueryParam trGrantType
+      , Map.singleton "assertion" (bs8ToLazyText trAssertion)
+      ]
+
+instance HasUserInfoRequest JwtBearerApplication
diff --git a/src/Network/OAuth2/Experiment/Grants/ResourceOwnerPassword.hs b/src/Network/OAuth2/Experiment/Grants/ResourceOwnerPassword.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Grants/ResourceOwnerPassword.hs
@@ -0,0 +1,78 @@
+{-# LANGUAGE FlexibleInstances #-}
+
+module Network.OAuth2.Experiment.Grants.ResourceOwnerPassword where
+
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Set (Set)
+import Data.Text.Lazy (Text)
+import Network.OAuth2 (ClientAuthenticationMethod (..))
+import Network.OAuth2 qualified as OAuth2
+import Network.OAuth2.Experiment.Flows.RefreshTokenRequest
+import Network.OAuth2.Experiment.Flows.TokenRequest
+import Network.OAuth2.Experiment.Flows.UserInfoRequest
+import Network.OAuth2.Experiment.Types
+
+-- | An Application that supports "Resource Owner Password" flow
+--
+-- https://www.rfc-editor.org/rfc/rfc6749#section-4.3
+data ResourceOwnerPasswordApplication = ResourceOwnerPasswordApplication
+  { ropClientId :: ClientId
+  , ropClientSecret :: ClientSecret
+  , ropName :: Text
+  , ropScope :: Set Scope
+  , ropUserName :: Username
+  , ropPassword :: Password
+  , ropTokenRequestExtraParams :: Map Text Text
+  , ropClientAuthenticationMethod :: ClientAuthenticationMethod
+  }
+
+instance HasClientAuthenticationMethod ResourceOwnerPasswordApplication where
+  getClientAuthenticationMethod :: ResourceOwnerPasswordApplication -> ClientAuthenticationMethod
+  getClientAuthenticationMethod = ropClientAuthenticationMethod
+  addClientAuthToHeader ResourceOwnerPasswordApplication {..} = addSecretToHeader ropClientId ropClientSecret
+
+-- | https://www.rfc-editor.org/rfc/rfc6749#section-4.3.2
+instance HasTokenRequest ResourceOwnerPasswordApplication where
+  type ExchangeTokenInfo ResourceOwnerPasswordApplication = NoNeedExchangeToken
+
+  data TokenRequest ResourceOwnerPasswordApplication = PasswordTokenRequest
+    { trScope :: Set Scope
+    , trUsername :: Username
+    , trPassword :: Password
+    , trGrantType :: GrantTypeValue
+    , trExtraParams :: Map Text Text
+    }
+  mkTokenRequestParam :: ResourceOwnerPasswordApplication -> NoNeedExchangeToken -> TokenRequest ResourceOwnerPasswordApplication
+  mkTokenRequestParam ResourceOwnerPasswordApplication {..} _ =
+    PasswordTokenRequest
+      { trUsername = ropUserName
+      , trPassword = ropPassword
+      , trGrantType = GTPassword
+      , trScope = ropScope
+      , trExtraParams = ropTokenRequestExtraParams
+      }
+
+instance ToQueryParam (TokenRequest ResourceOwnerPasswordApplication) where
+  toQueryParam :: TokenRequest ResourceOwnerPasswordApplication -> Map Text Text
+  toQueryParam PasswordTokenRequest {..} =
+    Map.unions
+      [ toQueryParam trGrantType
+      , toQueryParam trScope
+      , toQueryParam trUsername
+      , toQueryParam trPassword
+      , trExtraParams
+      ]
+
+instance HasUserInfoRequest ResourceOwnerPasswordApplication
+
+instance HasRefreshTokenRequest ResourceOwnerPasswordApplication where
+  mkRefreshTokenRequestParam :: ResourceOwnerPasswordApplication -> OAuth2.RefreshToken -> RefreshTokenRequest
+  mkRefreshTokenRequestParam ResourceOwnerPasswordApplication {..} rt =
+    RefreshTokenRequest
+      { rrScope = ropScope
+      , rrGrantType = GTRefreshToken
+      , rrRefreshToken = rt
+      , rrClientId = if ropClientAuthenticationMethod == ClientSecretPost then Just ropClientId else Nothing
+      , rrClientSecret = if ropClientAuthenticationMethod == ClientSecretPost then Just ropClientSecret else Nothing
+      }
diff --git a/src/Network/OAuth2/Experiment/Pkce.hs b/src/Network/OAuth2/Experiment/Pkce.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Pkce.hs
@@ -0,0 +1,82 @@
+module Network.OAuth2.Experiment.Pkce (
+  mkPkceParam,
+  CodeChallenge (..),
+  CodeVerifier (..),
+  CodeChallengeMethod (..),
+  PkceRequestParam (..),
+) where
+
+import Control.Monad.IO.Class
+import Crypto.Hash qualified as H
+import Crypto.Random qualified as Crypto
+import Data.Base64.Types qualified as B64
+import Data.ByteArray qualified as ByteArray
+import Data.ByteString qualified as BS
+import Data.ByteString.Base64.URL qualified as B64
+import Data.Text (Text)
+import Data.Text.Encoding qualified as T
+import Data.Word
+
+newtype CodeChallenge = CodeChallenge {unCodeChallenge :: Text}
+
+newtype CodeVerifier = CodeVerifier {unCodeVerifier :: Text}
+
+data CodeChallengeMethod = S256
+  deriving (Show)
+
+data PkceRequestParam = PkceRequestParam
+  { codeVerifier :: CodeVerifier
+  , codeChallenge :: CodeChallenge
+  , codeChallengeMethod :: CodeChallengeMethod
+  -- ^ spec says optional but in practice it is S256
+  -- https://datatracker.ietf.org/doc/html/rfc7636#section-4.3
+  }
+
+mkPkceParam :: MonadIO m => m PkceRequestParam
+mkPkceParam = do
+  codeV <- genCodeVerifier
+  pure
+    PkceRequestParam
+      { codeVerifier = CodeVerifier (T.decodeUtf8 codeV)
+      , codeChallenge = CodeChallenge (encodeCodeVerifier codeV)
+      , codeChallengeMethod = S256
+      }
+
+encodeCodeVerifier :: BS.ByteString -> Text
+encodeCodeVerifier = B64.extractBase64 . B64.encodeBase64Unpadded . BS.pack . ByteArray.unpack . hashSHA256
+
+genCodeVerifier :: MonadIO m => m BS.ByteString
+genCodeVerifier = liftIO $ getBytesInternal BS.empty
+
+cvMaxLen :: Int
+cvMaxLen = 128
+
+-- The default 'getRandomBytes' generates bytes out of unreverved characters scope.
+-- code-verifier = 43*128unreserved
+--   unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
+--   ALPHA = %x41-5A / %x61-7A
+--   DIGIT = %x30-39
+getBytesInternal :: BS.ByteString -> IO BS.ByteString
+getBytesInternal ba
+  | BS.length ba >= cvMaxLen = pure (BS.take cvMaxLen ba)
+  | otherwise = do
+      bs <- Crypto.getRandomBytes cvMaxLen
+      let bsUnreserved = ba `BS.append` BS.filter isUnreversed bs
+      getBytesInternal bsUnreserved
+
+hashSHA256 :: BS.ByteString -> H.Digest H.SHA256
+hashSHA256 = H.hash
+
+isUnreversed :: Word8 -> Bool
+isUnreversed w = w `BS.elem` unreverseBS
+
+{-
+a-z: 97-122
+A-Z: 65-90
+-: 45
+.: 46
+_: 95
+~: 126
+-}
+unreverseBS :: BS.ByteString
+unreverseBS = BS.pack $ [97 .. 122] ++ [65 .. 90] ++ [45, 46, 95, 126]
diff --git a/src/Network/OAuth2/Experiment/Types.hs b/src/Network/OAuth2/Experiment/Types.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Types.hs
@@ -0,0 +1,218 @@
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE RankNTypes #-}
+
+module Network.OAuth2.Experiment.Types where
+
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Set (Set)
+import Data.Set qualified as Set
+import Data.String
+import Data.Text.Lazy (Text)
+import Data.Text.Lazy qualified as TL
+import Network.OAuth2 hiding (RefreshToken)
+import Network.OAuth2 qualified as OAuth2
+import Network.OAuth2.Experiment.Pkce
+import Network.OAuth2.Experiment.Utils
+import URI.ByteString (URI, serializeURIRef')
+
+-------------------------------------------------------------------------------
+
+-- * Idp App
+
+-------------------------------------------------------------------------------
+
+-- | @Idp i@ consists various endpoints endpoints.
+--
+-- The @i@ is actually phantom type for information only (Idp name) at this moment.
+-- And it is PolyKinds.
+--
+-- Hence whenever @Idp i@ or @IdpApplication i a@ is used as function parameter,
+-- PolyKinds need to be enabled.
+data Idp (i :: k) = Idp
+  { idpUserInfoEndpoint :: URI
+  -- ^ Userinfo Endpoint
+  , idpAuthorizeEndpoint :: URI
+  -- ^ Authorization Endpoint
+  , idpTokenEndpoint :: URI
+  -- ^ Token Endpoint
+  , idpDeviceAuthorizationEndpoint :: Maybe URI
+  -- ^ Apparently not all IdP support device code flow
+  }
+
+-- | An OAuth2 Application "a" of IdP "i".
+-- "a" can be one of following type:
+--
+-- * `Network.OAuth2.Experiment.AuthorizationCodeApplication`
+-- * `Network.OAuth2.Experiment.DeviceAuthorizationApplication`
+-- * `Network.OAuth2.Experiment.ClientCredentialsApplication`
+-- * `Network.OAuth2.Experiment.ResourceOwnerPasswordApplication`
+-- * `Network.OAuth2.Experiment.JwtBearerApplication`
+data IdpApplication (i :: k) a = IdpApplication
+  { idp :: Idp i
+  , application :: a
+  }
+
+-------------------------------------------------------------------------------
+
+-- * Scope
+
+-------------------------------------------------------------------------------
+
+-- TODO: What's best type for Scope?
+-- Use 'Text' isn't super type safe. All cannot specify some standard scopes like openid, email etc.
+-- But Following data type is not ideal as Idp would have lots of 'Custom Text'
+--
+-- @
+-- data Scope = OPENID | PROFILE | EMAIL | OFFLINE_ACCESS | Custom Text
+-- @
+--
+-- Would be nice to define Enum for standard Scope, plus allow user to define their own define (per Idp) and plugin somehow.
+newtype Scope = Scope {unScope :: Text}
+  deriving (Eq, Ord, Show)
+
+instance IsString Scope where
+  fromString :: String -> Scope
+  fromString = Scope . TL.pack
+
+-------------------------------------------------------------------------------
+
+-- * Grant Type value
+
+-------------------------------------------------------------------------------
+
+-- | Grant type query parameter has association with different GrantType flows but not completely strict.
+--
+-- e.g. Both AuthorizationCode and ResourceOwnerPassword flow could support refresh token flow.
+data GrantTypeValue
+  = GTAuthorizationCode
+  | GTPassword
+  | GTClientCredentials
+  | GTRefreshToken
+  | GTJwtBearer
+  | GTDeviceCode
+  deriving (Eq, Show)
+
+-------------------------------------------------------------------------------
+--                               Response Type                               --
+-------------------------------------------------------------------------------
+data ResponseType = Code
+
+-------------------------------------------------------------------------------
+
+-- * Credentials
+
+-------------------------------------------------------------------------------
+newtype ClientId = ClientId {unClientId :: Text}
+  deriving (Show, Eq, IsString)
+
+-- | Can be either "Client Secret" or JWT based on the client authentication method
+newtype ClientSecret = ClientSecret {unClientSecret :: Text}
+  deriving (Eq, IsString)
+
+newtype RedirectUri = RedirectUri {unRedirectUri :: URI}
+  deriving (Eq)
+
+newtype AuthorizeState = AuthorizeState {unAuthorizeState :: Text}
+  deriving (Eq)
+
+instance IsString AuthorizeState where
+  fromString :: String -> AuthorizeState
+  fromString = AuthorizeState . TL.pack
+
+newtype Username = Username {unUsername :: Text}
+  deriving (Eq)
+
+instance IsString Username where
+  fromString :: String -> Username
+  fromString = Username . TL.pack
+
+newtype Password = Password {unPassword :: Text}
+  deriving (Eq)
+
+instance IsString Password where
+  fromString :: String -> Password
+  fromString = Password . TL.pack
+
+-------------------------------------------------------------------------------
+
+-- * Query parameters
+
+-------------------------------------------------------------------------------
+class ToQueryParam a where
+  toQueryParam :: a -> Map Text Text
+
+instance ToQueryParam a => ToQueryParam (Maybe a) where
+  toQueryParam :: ToQueryParam a => Maybe a -> Map Text Text
+  toQueryParam Nothing = Map.empty
+  toQueryParam (Just a) = toQueryParam a
+
+instance ToQueryParam GrantTypeValue where
+  toQueryParam :: GrantTypeValue -> Map Text Text
+  toQueryParam x = Map.singleton "grant_type" (val x)
+    where
+      val :: GrantTypeValue -> Text
+      val GTAuthorizationCode = "authorization_code"
+      val GTPassword = "password"
+      val GTClientCredentials = "client_credentials"
+      val GTRefreshToken = "refresh_token"
+      val GTJwtBearer = "urn:ietf:params:oauth:grant-type:jwt-bearer"
+      val GTDeviceCode = "urn:ietf:params:oauth:grant-type:device_code"
+
+instance ToQueryParam ClientId where
+  toQueryParam :: ClientId -> Map Text Text
+  toQueryParam (ClientId i) = Map.singleton "client_id" i
+
+instance ToQueryParam ClientSecret where
+  toQueryParam :: ClientSecret -> Map Text Text
+  toQueryParam (ClientSecret x) = Map.singleton "client_secret" x
+
+instance ToQueryParam Username where
+  toQueryParam :: Username -> Map Text Text
+  toQueryParam (Username x) = Map.singleton "username" x
+
+instance ToQueryParam Password where
+  toQueryParam :: Password -> Map Text Text
+  toQueryParam (Password x) = Map.singleton "password" x
+
+instance ToQueryParam AuthorizeState where
+  toQueryParam :: AuthorizeState -> Map Text Text
+  toQueryParam (AuthorizeState x) = Map.singleton "state" x
+
+instance ToQueryParam RedirectUri where
+  toQueryParam (RedirectUri uri) = Map.singleton "redirect_uri" (bs8ToLazyText $ serializeURIRef' uri)
+
+instance ToQueryParam (Set Scope) where
+  toQueryParam :: Set Scope -> Map Text Text
+  toQueryParam = toScopeParam . Set.map unScope
+    where
+      toScopeParam :: IsString a => Set Text -> Map a Text
+      toScopeParam scope =
+        if Set.null scope
+          then Map.empty
+          else Map.singleton "scope" (TL.intercalate " " $ Set.toList scope)
+
+instance ToQueryParam CodeVerifier where
+  toQueryParam :: CodeVerifier -> Map Text Text
+  toQueryParam (CodeVerifier x) = Map.singleton "code_verifier" (TL.fromStrict x)
+
+instance ToQueryParam CodeChallenge where
+  toQueryParam :: CodeChallenge -> Map Text Text
+  toQueryParam (CodeChallenge x) = Map.singleton "code_challenge" (TL.fromStrict x)
+
+instance ToQueryParam CodeChallengeMethod where
+  toQueryParam :: CodeChallengeMethod -> Map Text Text
+  toQueryParam x = Map.singleton "code_challenge_method" (TL.pack $ show x)
+
+instance ToQueryParam ExchangeToken where
+  toQueryParam :: ExchangeToken -> Map Text Text
+  toQueryParam (ExchangeToken x) = Map.singleton "code" (TL.fromStrict x)
+
+instance ToQueryParam OAuth2.RefreshToken where
+  toQueryParam :: OAuth2.RefreshToken -> Map Text Text
+  toQueryParam (OAuth2.RefreshToken x) = Map.singleton "refresh_token" (TL.fromStrict x)
+
+instance ToQueryParam ResponseType where
+  toQueryParam :: ResponseType -> Map Text Text
+  toQueryParam Code = Map.singleton "response_type" "code"
diff --git a/src/Network/OAuth2/Experiment/Utils.hs b/src/Network/OAuth2/Experiment/Utils.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Experiment/Utils.hs
@@ -0,0 +1,27 @@
+module Network.OAuth2.Experiment.Utils where
+
+import Data.Bifunctor
+import Data.ByteString (ByteString)
+import Data.ByteString.Char8 qualified as BS8
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as Map
+import Data.Text qualified as T
+import Data.Text.Encoding qualified as T
+import Data.Text.Encoding qualified as TE
+import Data.Text.Lazy qualified as TL
+import URI.ByteString (URI, serializeURIRef')
+
+tlToBS :: TL.Text -> ByteString
+tlToBS = TE.encodeUtf8 . TL.toStrict
+
+bs8ToLazyText :: BS8.ByteString -> TL.Text
+bs8ToLazyText = TL.pack . BS8.unpack
+
+unionMapsToQueryParams :: [Map TL.Text TL.Text] -> [(ByteString, ByteString)]
+unionMapsToQueryParams =
+  map (bimap tlToBS tlToBS)
+    . Map.toList
+    . Map.unions
+
+uriToText :: URI -> T.Text
+uriToText = T.decodeUtf8 . serializeURIRef'
diff --git a/src/Network/OAuth2/HttpClient.hs b/src/Network/OAuth2/HttpClient.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/HttpClient.hs
@@ -0,0 +1,245 @@
+-- | Bindings for The OAuth 2.0 Authorization Framework: Bearer Token Usage
+-- RFC6750 <https://www.rfc-editor.org/rfc/rfc6750>
+module Network.OAuth2.HttpClient (
+  -- * AUTH requests
+  authGetJSON,
+  authGetBS,
+  authGetJSONWithAuthMethod,
+  authGetBSWithAuthMethod,
+  authPostJSON,
+  authPostBS,
+  authPostJSONWithAuthMethod,
+  authPostBSWithAuthMethod,
+
+  -- * Types
+  APIAuthenticationMethod (..),
+) where
+
+import Control.Monad.IO.Class (MonadIO (..))
+import Control.Monad.Trans.Except (ExceptT (..), throwE)
+import Data.Aeson (FromJSON)
+import Data.Aeson qualified as Aeson
+import Data.Aeson.Key qualified as Aeson
+import Data.Aeson.KeyMap qualified as Aeson
+import Data.ByteString.Char8 qualified as BS
+import Data.ByteString.Lazy.Char8 qualified as BSL
+import Data.Text.Encoding qualified as T
+import Lens.Micro (over)
+import Network.HTTP.Client.Conduit (applyBearerAuth)
+import Network.HTTP.Client.Contrib (handleResponse)
+import Network.HTTP.Conduit
+import Network.HTTP.Types qualified as HT
+import Network.OAuth2.Internal
+import URI.ByteString (URI, URIRef, queryL, queryPairsL)
+
+--------------------------------------------------
+
+-- * AUTH requests
+
+-- Making request with Access Token appended to Header, Request body or query string.
+--
+--------------------------------------------------
+
+-- | Conduct an authorized GET request and return response as JSON.
+--   Inject Access Token to Authorization Header.
+authGetJSON ::
+  (MonadIO m, FromJSON a) =>
+  -- | HTTP connection manager.
+  Manager ->
+  AccessToken ->
+  URI ->
+  -- | Response as JSON
+  ExceptT BSL.ByteString m a
+authGetJSON = authGetJSONWithAuthMethod AuthInRequestHeader
+
+-- | Conduct an authorized GET request and return response as JSON.
+--   Allow to specify how to append AccessToken.
+--
+-- @since 2.6.0
+authGetJSONWithAuthMethod ::
+  (MonadIO m, FromJSON a) =>
+  APIAuthenticationMethod ->
+  -- | HTTP connection manager.
+  Manager ->
+  AccessToken ->
+  URI ->
+  -- | Response as JSON
+  ExceptT BSL.ByteString m a
+authGetJSONWithAuthMethod authTypes manager t uri = do
+  resp <- authGetBSWithAuthMethod authTypes manager t uri
+  either (throwE . BSL.pack) return (Aeson.eitherDecode resp)
+
+-- | Conduct an authorized GET request.
+--   Inject Access Token to Authorization Header.
+authGetBS ::
+  MonadIO m =>
+  -- | HTTP connection manager.
+  Manager ->
+  AccessToken ->
+  URI ->
+  -- | Response as ByteString
+  ExceptT BSL.ByteString m BSL.ByteString
+authGetBS = authGetBSWithAuthMethod AuthInRequestHeader
+
+-- | Conduct an authorized GET request and return response as ByteString.
+--   Allow to specify how to append AccessToken.
+--
+-- @since 2.6.0
+authGetBSWithAuthMethod ::
+  MonadIO m =>
+  -- | Specify the way that how to append the 'AccessToken' in the request
+  APIAuthenticationMethod ->
+  -- | HTTP connection manager.
+  Manager ->
+  AccessToken ->
+  URI ->
+  -- | Response as ByteString
+  ExceptT BSL.ByteString m BSL.ByteString
+authGetBSWithAuthMethod authTypes manager token url = do
+  let appendToUrl = AuthInRequestQuery == authTypes
+  let appendToHeader = AuthInRequestHeader == authTypes
+  let uri = if appendToUrl then url `appendAccessToken` token else url
+  let upReq = updateRequestHeaders (if appendToHeader then Just token else Nothing) . setMethod HT.GET
+  req <- liftIO $ uriToRequest uri
+  authRequest req upReq manager
+
+-- | Conduct POST request and return response as JSON.
+--   Inject Access Token to Authorization Header.
+authPostJSON ::
+  (MonadIO m, FromJSON a) =>
+  -- | HTTP connection manager.
+  Manager ->
+  AccessToken ->
+  URI ->
+  PostBody ->
+  -- | Response as JSON
+  ExceptT BSL.ByteString m a
+authPostJSON = authPostJSONWithAuthMethod AuthInRequestHeader
+
+-- | Conduct POST request and return response as JSON.
+--   Allow to specify how to append AccessToken.
+--
+-- @since 2.6.0
+authPostJSONWithAuthMethod ::
+  (MonadIO m, FromJSON a) =>
+  APIAuthenticationMethod ->
+  -- | HTTP connection manager.
+  Manager ->
+  AccessToken ->
+  URI ->
+  PostBody ->
+  -- | Response as ByteString
+  ExceptT BSL.ByteString m a
+authPostJSONWithAuthMethod authTypes manager token url body = do
+  resp <- authPostBSWithAuthMethod authTypes manager token url body
+  either (throwE . BSL.pack) return (Aeson.eitherDecode resp)
+
+-- | Conduct POST request.
+--   Inject Access Token to http header (Authorization)
+authPostBS ::
+  MonadIO m =>
+  -- | HTTP connection manager.
+  Manager ->
+  AccessToken ->
+  URI ->
+  PostBody ->
+  -- | Response as ByteString
+  ExceptT BSL.ByteString m BSL.ByteString
+authPostBS = authPostBSWithAuthMethod AuthInRequestHeader
+
+-- | Conduct POST request and return response as ByteString.
+--   Allow to specify how to append AccessToken.
+--
+-- @since 2.6.0
+authPostBSWithAuthMethod ::
+  MonadIO m =>
+  APIAuthenticationMethod ->
+  -- | HTTP connection manager.
+  Manager ->
+  AccessToken ->
+  URI ->
+  PostBody ->
+  -- | Response as ByteString
+  ExceptT BSL.ByteString m BSL.ByteString
+authPostBSWithAuthMethod authTypes manager token url body = do
+  let appendToBody = AuthInRequestBody == authTypes
+  let appendToHeader = AuthInRequestHeader == authTypes
+  let reqBody = if appendToBody then body ++ accessTokenToParam token else body
+  let upBody = if null reqBody then id else jsonBody reqBody
+  let upHeaders = updateRequestHeaders (if appendToHeader then Just token else Nothing) . setMethod HT.POST
+  let upReq = upHeaders . upBody
+
+  req <- liftIO $ uriToRequest url
+  authRequest req upReq manager
+
+jsonBody :: PostBody -> Request -> Request
+jsonBody body req =
+  req
+    { requestBody =
+        RequestBodyLBS $
+          Aeson.encode $
+            Aeson.fromList $
+              fmap (\(a, b) -> (Aeson.fromText (T.decodeUtf8 a), T.decodeUtf8 b)) body
+    , requestHeaders =
+        (HT.hContentType, "application/json")
+          : filter (\(x, _) -> x /= HT.hContentType) (requestHeaders req)
+    }
+
+--------------------------------------------------
+
+-- * Types
+
+--------------------------------------------------
+
+-- | https://www.rfc-editor.org/rfc/rfc6750#section-2
+data APIAuthenticationMethod
+  = -- | Provides in Authorization header
+    AuthInRequestHeader
+  | -- | Provides in request body
+    AuthInRequestBody
+  | -- | Provides in request query parameter
+    AuthInRequestQuery
+  deriving (Eq, Ord)
+
+--------------------------------------------------
+
+-- * Utilities
+
+--------------------------------------------------
+
+-- | Send an HTTP request.
+authRequest ::
+  MonadIO m =>
+  -- | Request to perform
+  Request ->
+  -- | Modify request before sending
+  (Request -> Request) ->
+  -- | HTTP connection manager.
+  Manager ->
+  ExceptT BSL.ByteString m BSL.ByteString
+authRequest req upReq manage = ExceptT $ do
+  resp <- httpLbs (upReq req) manage
+  pure (handleResponse resp)
+
+updateRequestHeaders :: Maybe AccessToken -> Request -> Request
+updateRequestHeaders mt =
+  maybe id (applyBearerAuth . T.encodeUtf8 . atoken) mt
+    . addDefaultRequestHeaders
+
+-- | Set the HTTP method to use.
+setMethod :: HT.StdMethod -> Request -> Request
+setMethod m req = req {method = HT.renderStdMethod m}
+
+-- | For @GET@ method API.
+appendAccessToken ::
+  -- | Base URI
+  URIRef a ->
+  -- | Authorized Access Token
+  AccessToken ->
+  -- | Combined Result
+  URIRef a
+appendAccessToken uri t = over (queryL . queryPairsL) (\query -> query ++ accessTokenToParam t) uri
+
+-- | Create `QueryParams` with given access token value.
+accessTokenToParam :: AccessToken -> [(BS.ByteString, BS.ByteString)]
+accessTokenToParam t = [("access_token", T.encodeUtf8 $ atoken t)]
diff --git a/src/Network/OAuth2/Internal.hs b/src/Network/OAuth2/Internal.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/Internal.hs
@@ -0,0 +1,116 @@
+{-# LANGUAGE QuasiQuotes #-}
+
+module Network.OAuth2.Internal where
+
+import Control.Monad.Catch
+import Data.Aeson
+import Data.Binary.Instances.Aeson ()
+import Data.ByteString qualified as BS
+import Data.ByteString.Char8 qualified as BS8
+import Data.Default
+import Data.Text (Text)
+import Data.Text qualified as T
+import Data.Text.Encoding qualified as T
+import Data.Version (showVersion)
+import Lens.Micro (over)
+import Network.HTTP.Conduit as C
+import Network.HTTP.Types qualified as HT
+import Paths_hoauth2 (version)
+import URI.ByteString
+import URI.ByteString.Aeson ()
+import URI.ByteString.QQ
+
+-------------------------------------------------------------------------------
+
+-- * OAuth2 Configuration
+
+-------------------------------------------------------------------------------
+
+-- | Query Parameter Representation
+data OAuth2 = OAuth2
+  { oauth2ClientId :: Text
+  , oauth2ClientSecret :: Text
+  , oauth2AuthorizeEndpoint :: URIRef Absolute
+  , oauth2TokenEndpoint :: URIRef Absolute
+  , oauth2RedirectUri :: URIRef Absolute
+  }
+  deriving (Show, Eq)
+
+instance Default OAuth2 where
+  def =
+    OAuth2
+      { oauth2ClientId = ""
+      , oauth2ClientSecret = ""
+      , oauth2AuthorizeEndpoint = [uri|https://www.example.com/|]
+      , oauth2TokenEndpoint = [uri|https://www.example.com/|]
+      , oauth2RedirectUri = [uri|https://www.example.com/|]
+      }
+
+-------------------------------------------------------------------------------
+
+-- * Tokens
+
+-------------------------------------------------------------------------------
+
+newtype AccessToken = AccessToken {atoken :: Text} deriving (Eq, Show, FromJSON, ToJSON)
+
+newtype RefreshToken = RefreshToken {rtoken :: Text} deriving (Eq, Show, FromJSON, ToJSON)
+
+newtype IdToken = IdToken {idtoken :: Text} deriving (Eq, Show, FromJSON, ToJSON)
+
+-- | Authorization Code
+newtype ExchangeToken = ExchangeToken {extoken :: Text} deriving (Show, FromJSON, ToJSON)
+
+-------------------------------------------------------------------------------
+
+-- * Client Authentication methods
+
+-------------------------------------------------------------------------------
+
+-- | How would the Client (RP) authenticate itself?
+--
+-- The client MUST NOT use more than one authentication method in each request.
+-- Means use Authorization header or Post body.
+--
+-- See more details
+--
+-- https://www.rfc-editor.org/rfc/rfc6749#section-2.3
+-- https://oauth.net/private-key-jwt/
+-- https://www.rfc-editor.org/rfc/rfc7523.html
+data ClientAuthenticationMethod
+  = ClientSecretBasic
+  | ClientSecretPost
+  | ClientAssertionJwt
+  deriving (Eq, Show)
+
+-------------------------------------------------------------------------------
+
+-- * Utilies for Request and URI
+
+-------------------------------------------------------------------------------
+
+-- | Type synonym of post body content
+type PostBody = [(BS.ByteString, BS.ByteString)]
+
+-- | Type sysnonym of request query params
+type QueryParams = [(BS.ByteString, BS.ByteString)]
+
+defaultRequestHeaders :: [(HT.HeaderName, BS.ByteString)]
+defaultRequestHeaders =
+  [ (HT.hUserAgent, "hoauth2-" <> (T.encodeUtf8 . T.pack $ showVersion version))
+  , (HT.hAccept, "application/json")
+  ]
+
+-- | Set several header values:
+--   + userAgennt    : "hoauth2"
+--   + accept        : "application/json"
+addDefaultRequestHeaders :: Request -> Request
+addDefaultRequestHeaders req =
+  let headers = defaultRequestHeaders ++ requestHeaders req
+   in req {requestHeaders = headers}
+
+appendQueryParams :: [(BS.ByteString, BS.ByteString)] -> URIRef a -> URIRef a
+appendQueryParams params = over (queryL . queryPairsL) (params ++)
+
+uriToRequest :: MonadThrow m => URI -> m Request
+uriToRequest = parseRequest . BS8.unpack . serializeURIRef'
diff --git a/src/Network/OAuth2/TokenRequest.hs b/src/Network/OAuth2/TokenRequest.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/OAuth2/TokenRequest.hs
@@ -0,0 +1,362 @@
+-- | Bindings Access Token and Refresh Token part of The OAuth 2.0 Authorization Framework
+-- RFC6749 <https://www.rfc-editor.org/rfc/rfc6749>
+module Network.OAuth2.TokenRequest where
+
+import Control.Monad.IO.Class (MonadIO (..))
+import Control.Monad.Trans.Except (ExceptT (..), throwE)
+import Data.Aeson
+import Data.Aeson qualified as Aeson
+import Data.Aeson.Key qualified as Key
+import Data.Aeson.KeyMap qualified as KeyMap
+import Data.Aeson.Types (Parser, explicitParseFieldMaybe)
+import Data.Binary (Binary (..))
+import Data.Binary.Instances.Aeson ()
+import Data.ByteString.Lazy.Char8 qualified as BSL
+import Data.Text (Text, unpack)
+import Data.Text qualified as T
+import Data.Text.Encoding qualified as T
+import Network.HTTP.Conduit
+import Network.HTTP.Types qualified as HT
+import Network.HTTP.Types.URI (parseQuery)
+import Network.OAuth2.Internal
+import URI.ByteString
+import Prelude hiding (error)
+
+--------------------------------------------------
+
+-- * Token Request Errors
+
+--------------------------------------------------
+
+data TokenResponseError = TokenResponseError
+  { tokenResponseError :: TokenResponseErrorCode
+  , tokenResponseErrorDescription :: Maybe Text
+  , tokenResponseErrorUri :: Maybe (URIRef Absolute)
+  }
+  deriving (Show, Eq)
+
+-- | Token Error Responses https://tools.ietf.org/html/rfc6749#section-5.2
+data TokenResponseErrorCode
+  = InvalidRequest
+  | InvalidClient
+  | InvalidGrant
+  | UnauthorizedClient
+  | UnsupportedGrantType
+  | InvalidScope
+  | UnknownErrorCode Text
+  deriving (Show, Eq)
+
+instance FromJSON TokenResponseErrorCode where
+  parseJSON = withText "parseJSON TokenResponseErrorCode" $ \t ->
+    pure $ case t of
+      "invalid_request" -> InvalidRequest
+      "invalid_client" -> InvalidClient
+      "invalid_grant" -> InvalidGrant
+      "unauthorized_client" -> UnauthorizedClient
+      "unsupported_grant_type" -> UnsupportedGrantType
+      "invalid_scope" -> InvalidScope
+      _ -> UnknownErrorCode t
+
+instance FromJSON TokenResponseError where
+  parseJSON = withObject "parseJSON TokenResponseError" $ \t -> do
+    tokenResponseError <- t .: "error"
+    tokenResponseErrorDescription <- t .:? "error_description"
+    tokenResponseErrorUri <- t .:? "error_uri"
+    pure TokenResponseError {..}
+
+parseTokeResponseError :: BSL.ByteString -> TokenResponseError
+parseTokeResponseError string =
+  either (mkDecodeOAuth2Error string) id (eitherDecode string)
+  where
+    mkDecodeOAuth2Error :: BSL.ByteString -> String -> TokenResponseError
+    mkDecodeOAuth2Error response err =
+      TokenResponseError
+        (UnknownErrorCode "")
+        (Just $ T.pack $ "Decode TokenResponseError failed: " <> err <> "\n Original Response:\n" <> show (T.decodeUtf8 $ BSL.toStrict response))
+        Nothing
+
+-------------------------------------------------------------------------------
+
+-- * Tokens
+
+-------------------------------------------------------------------------------
+
+-- | https://www.rfc-editor.org/rfc/rfc6749#section-4.1.4
+data TokenResponse = TokenResponse
+  { accessToken :: AccessToken
+  , refreshToken :: Maybe RefreshToken
+  -- ^ Exists when @offline_access@ scope is in the Authorization Request and the provider supports Refresh Access Token.
+  , expiresIn :: Maybe Int
+  , tokenType :: Maybe Text
+  -- ^ See https://www.rfc-editor.org/rfc/rfc6749#section-5.1. It's required by spec, but OAuth2 provider implementations vary. We may remove 'Maybe' in a future release.
+  , idToken :: Maybe IdToken
+  -- ^ Exists when @openid@ scope is in the Authorization Request and the provider supports OpenID protocol.
+  , scope :: Maybe Text
+  , rawResponse :: Object
+  }
+  deriving (Eq)
+
+instance Show TokenResponse where
+  show TokenResponse {..} =
+    "TokenResponse {"
+      <> "access_token = ***"
+      <> ", id_token = "
+      <> showM idToken
+      <> ", refresh_token = "
+      <> showM refreshToken
+      <> ", expires_in = "
+      <> show expiresIn
+      <> ", token_type = "
+      <> show tokenType
+      <> ", scope = "
+      <> show scope
+      <> ", raw_response = ***"
+      <> "}"
+    where
+      showM (Just _) = "***"
+      showM Nothing = "Nothing"
+
+instance Binary TokenResponse where
+  put TokenResponse {..} = put rawResponse
+  get = do
+    rawt <- get
+    case fromJSON (Aeson.Object rawt) of
+      Success a -> pure a
+      Error err -> fail err
+
+-- | Parse JSON data into 'TokenResponse'
+instance FromJSON TokenResponse where
+  parseJSON :: Value -> Parser TokenResponse
+  parseJSON = withObject "TokenResponse" $ \v ->
+    TokenResponse
+      <$> v .: "access_token"
+      <*> v .:? "refresh_token"
+      <*> explicitParseFieldMaybe parseIntFlexible v "expires_in"
+      <*> v .:? "token_type"
+      <*> v .:? "id_token"
+      <*> v .:? "scope"
+      <*> pure v
+    where
+      parseIntFlexible :: Value -> Parser Int
+      parseIntFlexible (String s) = pure . read $ unpack s
+      parseIntFlexible v = parseJSON v
+
+instance ToJSON TokenResponse where
+  toJSON :: TokenResponse -> Value
+  toJSON = toJSON . Object . rawResponse
+  toEncoding :: TokenResponse -> Encoding
+  toEncoding = toEncoding . Object . rawResponse
+
+--------------------------------------------------
+
+-- * URL
+
+--------------------------------------------------
+
+-- | Prepare the URL and the request body query for fetching an access token.
+accessTokenUrl ::
+  OAuth2 ->
+  -- | access code gained via authorization URL
+  ExchangeToken ->
+  -- | access token request URL plus the request body.
+  (URI, PostBody)
+accessTokenUrl oa code =
+  let uri = oauth2TokenEndpoint oa
+      body =
+        [ ("code", T.encodeUtf8 $ extoken code)
+        , ("redirect_uri", serializeURIRef' $ oauth2RedirectUri oa)
+        , ("grant_type", "authorization_code")
+        ]
+   in (uri, body)
+
+-- | Obtain a new access token by sending a Refresh Token to the Authorization server.
+refreshAccessTokenUrl ::
+  OAuth2 ->
+  -- | Refresh Token gained via authorization URL
+  RefreshToken ->
+  -- | Refresh Token request URL plus the request body.
+  (URI, PostBody)
+refreshAccessTokenUrl oa token = (uri, body)
+  where
+    uri = oauth2TokenEndpoint oa
+    body =
+      [ ("grant_type", "refresh_token")
+      , ("refresh_token", T.encodeUtf8 $ rtoken token)
+      ]
+
+--------------------------------------------------
+
+-- * Token management
+
+--------------------------------------------------
+
+-- | Exchange @code@ for an Access Token with authenticate in request header.
+fetchAccessToken ::
+  MonadIO m =>
+  -- | HTTP connection manager
+  Manager ->
+  -- | OAuth Data
+  OAuth2 ->
+  -- | OAuth2 Code
+  ExchangeToken ->
+  -- | Access Token
+  ExceptT TokenResponseError m TokenResponse
+fetchAccessToken = fetchAccessTokenWithAuthMethod ClientSecretBasic
+
+-- | Exchange @code@ for an Access Token
+--
+-- OAuth2 spec allows credential (@client_id@, @client_secret@) to be sent
+-- either in the header (a.k.a `ClientSecretBasic`).
+-- or as form/url params (a.k.a `ClientSecretPost`).
+--
+-- The OAuth provider can choose to implement only one, or both.
+-- Look for API document from the OAuth provider you're dealing with.
+-- If you`re uncertain, try `fetchAccessToken` which sends credential
+-- in authorization http header, which is common case.
+--
+-- @since 2.6.0
+fetchAccessTokenWithAuthMethod ::
+  MonadIO m =>
+  ClientAuthenticationMethod ->
+  -- | HTTP connection manager
+  Manager ->
+  -- | OAuth Data
+  OAuth2 ->
+  -- | Authorization Code
+  ExchangeToken ->
+  -- | Access Token
+  ExceptT TokenResponseError m TokenResponse
+fetchAccessTokenWithAuthMethod authMethod manager oa code = do
+  let (uri, body) = accessTokenUrl oa code
+  let extraBody = if authMethod == ClientSecretPost then clientSecretPost oa else []
+  doJSONPostRequest manager oa uri (body ++ extraBody)
+
+-- | Fetch a new AccessToken using the Refresh Token with authentication in request header.
+refreshAccessToken ::
+  MonadIO m =>
+  -- | HTTP connection manager.
+  Manager ->
+  -- | OAuth context
+  OAuth2 ->
+  -- | Refresh Token gained after authorization
+  RefreshToken ->
+  ExceptT TokenResponseError m TokenResponse
+refreshAccessToken = refreshAccessTokenWithAuthMethod ClientSecretBasic
+
+-- | Fetch a new AccessToken using the Refresh Token.
+--
+-- OAuth2 spec allows credential ("client_id", "client_secret") to be sent
+-- either in the header (a.k.a 'ClientSecretBasic').
+-- or as form/url params (a.k.a 'ClientSecretPost').
+--
+-- The OAuth provider can choose to implement only one, or both.
+-- Look for API document from the OAuth provider you're dealing with.
+-- If you're uncertain, try 'refreshAccessToken' which sends credential
+-- in authorization http header, which is common case.
+--
+-- @since 2.6.0
+refreshAccessTokenWithAuthMethod ::
+  MonadIO m =>
+  ClientAuthenticationMethod ->
+  -- | HTTP connection manager.
+  Manager ->
+  -- | OAuth context
+  OAuth2 ->
+  -- | Refresh Token gained after authorization
+  RefreshToken ->
+  ExceptT TokenResponseError m TokenResponse
+refreshAccessTokenWithAuthMethod authMethod manager oa token = do
+  let (uri, body) = refreshAccessTokenUrl oa token
+  let extraBody = if authMethod == ClientSecretPost then clientSecretPost oa else []
+  doJSONPostRequest manager oa uri (body ++ extraBody)
+
+--------------------------------------------------
+
+-- * Utilies
+
+--------------------------------------------------
+
+-- | Conduct post request and return response as JSON.
+doJSONPostRequest ::
+  (MonadIO m, FromJSON a) =>
+  -- | HTTP connection manager.
+  Manager ->
+  -- | OAuth options
+  OAuth2 ->
+  -- | The URL
+  URI ->
+  -- | request body
+  PostBody ->
+  -- | Response as JSON
+  ExceptT TokenResponseError m a
+doJSONPostRequest manager oa uri body = do
+  resp <- doSimplePostRequest manager oa uri body
+  case parseResponseFlexible resp of
+    Right obj -> return obj
+    Left e -> throwE e
+
+-- | Conduct post request.
+doSimplePostRequest ::
+  MonadIO m =>
+  -- | HTTP connection manager.
+  Manager ->
+  -- | OAuth options
+  OAuth2 ->
+  -- | URL
+  URI ->
+  -- | Request body.
+  PostBody ->
+  -- | Response as ByteString
+  ExceptT TokenResponseError m BSL.ByteString
+doSimplePostRequest manager oa url body =
+  ExceptT . liftIO $ fmap handleOAuth2TokenResponse go
+  where
+    go = do
+      req <- uriToRequest url
+      let req' = (addBasicAuth oa . addDefaultRequestHeaders) req
+      httpLbs (urlEncodedBody body req') manager
+
+-- | Gets response body from a @Response@ if 200 otherwise assume 'Network.OAuth2.TokenRequest.TokenResponseError'
+handleOAuth2TokenResponse :: Response BSL.ByteString -> Either TokenResponseError BSL.ByteString
+handleOAuth2TokenResponse rsp =
+  if HT.statusIsSuccessful (responseStatus rsp)
+    then Right $ responseBody rsp
+    else Left $ parseTokeResponseError (responseBody rsp)
+
+-- | Try to parses response as JSON, if failed, try to parse as like query string.
+parseResponseFlexible ::
+  FromJSON a =>
+  BSL.ByteString ->
+  Either TokenResponseError a
+parseResponseFlexible r = case eitherDecode r of
+  Left _ -> parseResponseString r
+  Right x -> Right x
+
+-- | Parses the response that contains not JSON but a Query String
+parseResponseString ::
+  FromJSON a =>
+  BSL.ByteString ->
+  Either TokenResponseError a
+parseResponseString b = case parseQuery $ BSL.toStrict b of
+  [] -> Left errorMessage
+  a -> case fromJSON $ queryToValue a of
+    Error _ -> Left errorMessage
+    Success x -> Right x
+  where
+    queryToValue = Object . KeyMap.fromList . map paramToPair
+    paramToPair (k, mv) = (Key.fromText $ T.decodeUtf8 k, maybe Null (String . T.decodeUtf8) mv)
+    errorMessage = parseTokeResponseError b
+
+-- | Add Basic Authentication header using client_id and client_secret.
+addBasicAuth :: OAuth2 -> Request -> Request
+addBasicAuth oa =
+  applyBasicAuth
+    (T.encodeUtf8 $ oauth2ClientId oa)
+    (T.encodeUtf8 $ oauth2ClientSecret oa)
+
+-- | Add Credential (client_id, client_secret) to the request post body.
+clientSecretPost :: OAuth2 -> PostBody
+clientSecretPost oa =
+  [ ("client_id", T.encodeUtf8 $ oauth2ClientId oa)
+  , ("client_secret", T.encodeUtf8 $ oauth2ClientSecret oa)
+  ]
diff --git a/test/Network/OAuth2/InternalSpec.hs b/test/Network/OAuth2/InternalSpec.hs
new file mode 100644
--- /dev/null
+++ b/test/Network/OAuth2/InternalSpec.hs
@@ -0,0 +1,69 @@
+{-# LANGUAGE QuasiQuotes #-}
+
+module Network.OAuth2.InternalSpec where
+
+import Control.Monad.IO.Class (MonadIO (..))
+import Network.HTTP.Conduit
+import Network.OAuth2
+import Test.Hspec
+import URI.ByteString.QQ
+
+spec :: Spec
+spec = do
+  describe "uriToRequest" $ do
+    it "parse http://localhost:3001/abc/foo?scope=openid&redirect_uri=http://localhost:3001/callback" $ do
+      req <- liftIO $ uriToRequest [uri|http://localhost:3001/abc/foo?scope=openid&&redirect_uri=http://localhost:3001/callback|]
+      secure req `shouldBe` False
+      path req `shouldBe` "/abc/foo"
+      port req `shouldBe` 3001
+      host req `shouldBe` "localhost"
+      queryString req `shouldBe` "?scope=openid&redirect_uri=http%3A%2F%2Flocalhost%3A3001%2Fcallback"
+    it "parse http://localhost:3001/abc/foo" $ do
+      req <- liftIO $ uriToRequest [uri|http://localhost:3001/abc/foo|]
+      secure req `shouldBe` False
+      path req `shouldBe` "/abc/foo"
+      port req `shouldBe` 3001
+      host req `shouldBe` "localhost"
+      queryString req `shouldBe` ""
+    it "parse http://localhost:3001/" $ do
+      req <- liftIO $ uriToRequest [uri|http://localhost:3001/|]
+      secure req `shouldBe` False
+      path req `shouldBe` "/"
+      port req `shouldBe` 3001
+      host req `shouldBe` "localhost"
+      queryString req `shouldBe` ""
+    it "parse https://test.auth0.com/authorize" $ do
+      req <- liftIO $ uriToRequest [uri|https://test.auth0.com/authorize|]
+      secure req `shouldBe` True
+      path req `shouldBe` "/authorize"
+      port req `shouldBe` 443
+      host req `shouldBe` "test.auth0.com"
+      queryString req `shouldBe` ""
+    it "parse URL with multiple query parameters" $ do
+      req <- liftIO $ uriToRequest [uri|https://api.example.com/oauth2/auth?client_id=123&scope=read,write&state=xyz|]
+      secure req `shouldBe` True
+      path req `shouldBe` "/oauth2/auth"
+      port req `shouldBe` 443
+      host req `shouldBe` "api.example.com"
+      queryString req `shouldBe` "?client_id=123&scope=read%2Cwrite&state=xyz"
+    it "parse URL with special characters in path" $ do
+      req <- liftIO $ uriToRequest [uri|https://api.example.com/oauth2/user+info/profile%20data|]
+      secure req `shouldBe` True
+      path req `shouldBe` "/oauth2/user+info/profile%20data"
+      port req `shouldBe` 443
+      host req `shouldBe` "api.example.com"
+      queryString req `shouldBe` ""
+    it "parse URL with fragments (which should be ignored)" $ do
+      req <- liftIO $ uriToRequest [uri|https://api.example.com/callback#access_token=xyz|]
+      secure req `shouldBe` True
+      path req `shouldBe` "/callback"
+      port req `shouldBe` 443
+      host req `shouldBe` "api.example.com"
+      queryString req `shouldBe` ""
+    it "parse URL with non-standard HTTPS port" $ do
+      req <- liftIO $ uriToRequest [uri|https://api.example.com:8443/oauth/token|]
+      secure req `shouldBe` True
+      path req `shouldBe` "/oauth/token"
+      port req `shouldBe` 8443
+      host req `shouldBe` "api.example.com"
+      queryString req `shouldBe` ""
diff --git a/test/Network/OAuth2/TokenRequestSpec.hs b/test/Network/OAuth2/TokenRequestSpec.hs
new file mode 100644
--- /dev/null
+++ b/test/Network/OAuth2/TokenRequestSpec.hs
@@ -0,0 +1,56 @@
+{-# LANGUAGE QuasiQuotes #-}
+
+module Network.OAuth2.TokenRequestSpec where
+
+import Data.Aeson qualified as Aeson
+import Network.OAuth2.TokenRequest
+import Test.Hspec
+import URI.ByteString.QQ
+import Prelude hiding (error)
+
+spec :: Spec
+spec = do
+  describe "parseJSON TokenResponseErrorCode" $ do
+    it "invalid_request" $ do
+      Aeson.eitherDecode "\"invalid_request\"" `shouldBe` Right InvalidRequest
+    it "invalid_client" $ do
+      Aeson.eitherDecode "\"invalid_client\"" `shouldBe` Right InvalidClient
+    it "invalid_grant" $ do
+      Aeson.eitherDecode "\"invalid_grant\"" `shouldBe` Right InvalidGrant
+    it "unauthorized_client" $ do
+      Aeson.eitherDecode "\"unauthorized_client\"" `shouldBe` Right UnauthorizedClient
+    it "unsupported_grant_type" $ do
+      Aeson.eitherDecode "\"unsupported_grant_type\"" `shouldBe` Right UnsupportedGrantType
+    it "invalid_scope" $ do
+      Aeson.eitherDecode "\"invalid_scope\"" `shouldBe` Right InvalidScope
+    it "foo_code" $ do
+      Aeson.eitherDecode "\"foo_code\"" `shouldBe` Right (UnknownErrorCode "foo_code")
+
+  describe "parseJSON TokenResponseError" $ do
+    it "parse error" $ do
+      Aeson.eitherDecode "{\"error\": \"invalid_request\"}"
+        `shouldBe` Right
+          ( TokenResponseError
+              { tokenResponseError = InvalidRequest
+              , tokenResponseErrorDescription = Nothing
+              , tokenResponseErrorUri = Nothing
+              }
+          )
+    it "parse error_description" $ do
+      Aeson.eitherDecode "{\"error\": \"invalid_request\", \"error_description\": \"token request error foo1\"}"
+        `shouldBe` Right
+          ( TokenResponseError
+              { tokenResponseError = InvalidRequest
+              , tokenResponseErrorDescription = Just "token request error foo1"
+              , tokenResponseErrorUri = Nothing
+              }
+          )
+    it "parse error_uri" $ do
+      Aeson.eitherDecode "{\"error\": \"invalid_request\", \"error_uri\": \"https://example.com\"}"
+        `shouldBe` Right
+          ( TokenResponseError
+              { tokenResponseError = InvalidRequest
+              , tokenResponseErrorDescription = Nothing
+              , tokenResponseErrorUri = Just [uri|https://example.com|]
+              }
+          )
diff --git a/test/Network/OAuth2/TokenResponseSpec.hs b/test/Network/OAuth2/TokenResponseSpec.hs
new file mode 100644
--- /dev/null
+++ b/test/Network/OAuth2/TokenResponseSpec.hs
@@ -0,0 +1,48 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeApplications #-}
+
+module Network.OAuth2.TokenResponseSpec where
+
+import Data.Aeson qualified as Aeson
+import Data.Binary qualified as Binary
+import Data.Maybe (fromJust)
+import Network.OAuth2 (AccessToken (..), RefreshToken (..), TokenResponse (..))
+import Test.Hspec
+
+spec :: Spec
+spec = do
+  describe "decode as JSON" $ do
+    it "parse access token" $ do
+      let resp = "{\"access_token\":\"ya29\",\"token_type\":\"Bearer\",\"expires_in\":3600,\"refresh_token\":\"0gk\"}"
+      Aeson.eitherDecode resp
+        `shouldBe` Right
+          ( TokenResponse
+              { accessToken = AccessToken "ya29"
+              , refreshToken = Just (RefreshToken "0gk")
+              , expiresIn = Just 3600
+              , tokenType = Just "Bearer"
+              , idToken = Nothing
+              , scope = Nothing
+              , rawResponse = fromJust (Aeson.decode resp)
+              }
+          )
+    it "parse access token with scope" $ do
+      let resp = "{\"access_token\":\"ya29\",\"token_type\":\"Bearer\",\"expires_in\":3600,\"refresh_token\":\"0gk\",\"scope\": \"openid profile\"}"
+      Aeson.eitherDecode resp
+        `shouldBe` Right
+          ( TokenResponse
+              { accessToken = AccessToken "ya29"
+              , refreshToken = Just (RefreshToken "0gk")
+              , expiresIn = Just 3600
+              , tokenType = Just "Bearer"
+              , idToken = Nothing
+              , scope = Just "openid profile"
+              , rawResponse = fromJust (Aeson.decode resp)
+              }
+          )
+  describe "encode/decode binary" $ do
+    it "support binary encoding" $ do
+      let resp = "{\"access_token\":\"ya29\",\"token_type\":\"Bearer\",\"expires_in\":3600,\"refresh_token\":\"0gk\"}"
+          oauth2Token = fromJust (Aeson.decode @TokenResponse resp)
+      Binary.decode @TokenResponse (Binary.encode oauth2Token)
+        `shouldBe` oauth2Token
diff --git a/test/Spec.hs b/test/Spec.hs
new file mode 100644
--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,2 @@
+-- file test/Spec.hs
+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}
