response.json

{
  "data": {
    "__type": {
      "kind": "UNION",
      "name": "TestUnion",
      "fields": null,
      "inputFields": null,
      "interfaces": null,
      "enumValues": null,
      "possibleTypes": [
        {
          "kind": "OBJECT",
          "name": "User",
          "ofType": null
        },
        {
          "kind": "OBJECT",
          "name": "Address",
          "ofType": null
        }
      ]
    }
  }
}