diff --git a/soap.cabal b/soap.cabal
--- a/soap.cabal
+++ b/soap.cabal
@@ -2,7 +2,7 @@
 -- see http://haskell.org/cabal/users-guide/
 
 name:                soap
-version:             0.1.0.1
+version:             0.1.0.3
 synopsis:            SOAP client tools
 description:         Tools to build SOAP clients using xml-conduit.
 homepage:            https://bitbucket.org/dpwiz/haskell-soap
@@ -17,13 +17,14 @@
 
 library
   hs-source-dirs:    src/
+  ghc-options: -Wall -O2
   exposed-modules:
     Web.SOAP.Service
     Web.SOAP.Types
 --  other-modules:
   build-depends:
     base ==4.*,
-    http-conduit,
+    http-conduit, resourcet, tls-extra,
     xml-conduit,
     iconv,
     text,
diff --git a/src/Web/SOAP/Service.hs b/src/Web/SOAP/Service.hs
--- a/src/Web/SOAP/Service.hs
+++ b/src/Web/SOAP/Service.hs
@@ -1,12 +1,15 @@
-{-# LANGUAGE OverloadedStrings, RecordWildCards #-}
+{-# LANGUAGE OverloadedStrings, RecordWildCards, Rank2Types, KindSignatures #-}
 module Web.SOAP.Service
     ( SOAPSettings(..)
     , invokeWS
+    , invokeWS'
     ) where
 
 import           Text.XML
 import           Text.XML.Cursor
 import           Network.HTTP.Conduit
+import           Control.Monad.Trans.Resource (ResourceT)
+
 import           Data.Text (Text)
 import qualified Data.Text as T
 import qualified Data.Text.Lazy as TL
@@ -25,7 +28,6 @@
     soapCodepage :: IC.EncodingName
 } deriving (Read, Show)
 
-
 -- | Query a SOAP service.
 invokeWS :: (ToNodes h, ToNodes i, FromCursor o)
          => SOAPSettings  -- ^ web service configuration
@@ -33,8 +35,17 @@
          -> h             -- ^ request headers
          -> i             -- ^ request body
          -> IO o          -- ^ response
+invokeWS = invokeWS' id
 
-invokeWS SOAPSettings{..} methodHeader h b = do
+-- | Query a SOAP service with a customized 'Request'.
+invokeWS' :: (ToNodes h, ToNodes i, FromCursor o)
+          => (Request (ResourceT IO) -> Request (ResourceT IO)) -- ^ request transformation to apply before sending
+          -> SOAPSettings  -- ^ web service configuration
+          -> Text          -- ^ SOAPAction header
+          -> h             -- ^ request headers
+          -> i             -- ^ request body
+          -> IO o          -- ^ response
+invokeWS' reqProc SOAPSettings{..} methodHeader h b = do
     let headerNodes = toNodes h
     let bodyNodes = map (flowNS $ Just soapNamespace) (toNodes b)
 
@@ -45,13 +56,14 @@
     TL.putStrLn . renderText def { rsPretty = True } $! doc
 
     request <- parseUrl soapURL
-    res <- withManager $ httpLbs request { method          = "POST"
-                                         , responseTimeout = Just 15000000
-                                         , requestBody     = RequestBodyLBS body
-                                         , requestHeaders  = [ ("Content-Type", "text/xml; charset=utf-8")
-                                                             , ("SOAPAction", TE.encodeUtf8 methodHeader)
-                                                             ]
-                                         }
+    let request' = request { method          = "POST"
+                           , responseTimeout = Just 15000000
+                           , requestBody     = RequestBodyLBS body
+                           , requestHeaders  = [ ("Content-Type", "text/xml; charset=utf-8")
+                                               , ("SOAPAction", TE.encodeUtf8 methodHeader)
+                                               ]
+                           }
+    res <- withManager $ httpLbs (reqProc request')
 
     let resBody = IC.convertFuzzy IC.Transliterate soapCodepage "utf-8" $ responseBody res
 
@@ -75,13 +87,16 @@
 document r = Document (Prologue [] Nothing []) r []
 
 envelope :: [Node] -> [Node] -> Element
-envelope h b =
+envelope header body =
     Element
         "{http://schemas.xmlsoap.org/soap/envelope/}Envelope"
         def
-        [ NodeElement $! Element "{http://schemas.xmlsoap.org/soap/envelope/}Header" def h
-        , NodeElement $! Element "{http://schemas.xmlsoap.org/soap/envelope/}Body" def b
-        ]
+        ( if null header
+            then [ NodeElement $! Element "{http://schemas.xmlsoap.org/soap/envelope/}Body" def body ]
+            else [ NodeElement $! Element "{http://schemas.xmlsoap.org/soap/envelope/}Header" def header
+                 , NodeElement $! Element "{http://schemas.xmlsoap.org/soap/envelope/}Body" def body
+                 ]
+        )
 
 -- | Little helper to apply default service namespace to body nodes and their descendants.
 --   This removes the necessity to flood your code with {http://vendor.silly.web/Service.spamx} in element names.