Don't allow webob to set a default content type

Webob sets the Content-Type of responses to 'text/html' if nothing else
is set. There are a number of bugs out for webob with this but it seems
unlikely it will be fixed upstream.

We don't want auth_token middleware automatically setting content-types
on application responses so create our own response object with an empty
default_content_type so it's not set.

Change-Id: I947f384e170a8d2685b71e1a6611c6241e827196
Closes-Bug: #1466499

keystonemiddleware/auth_token/_request.py

@@ -53,8 +53,17 @@ def _v3_to_v2_catalog(catalog):
     return v2_services
 
 
+# NOTE(jamielennox): this should probably be moved into its own file, but at
+# the moment there's no real logic here so just keep it locally.
+class _AuthTokenResponse(webob.Response):
+
+    default_content_type = None  # prevents webob assigning a content type
+
+
 class _AuthTokenRequest(webob.Request):
 
+    ResponseClass = _AuthTokenResponse
+
     _HEADER_TEMPLATE = {
         'X%s-Domain-Id': 'domain_id',
         'X%s-Domain-Name': 'domain_name',

keystonemiddleware/tests/unit/auth_token/test_auth_token_middleware.py

@@ -1321,6 +1321,29 @@ class CommonAuthTokenMiddlewareTest(object):
         self.assertFalse(token_auth.has_service_token)
         self.assertIsNone(token_auth.service)
 
+    def test_doesnt_auto_set_content_type(self):
+        # webob will set content_type = 'text/html' by default if nothing is
+        # provided. We don't want our middleware messing with the content type
+        # of the underlying applications.
+
+        text = uuid.uuid4().hex
+
+        def _middleware(environ, start_response):
+            start_response(200, [])
+            return text
+
+        def _start_response(status_code, headerlist, exc_info=None):
+            self.assertIn('200', status_code)  # will be '200 OK'
+            self.assertEqual([], headerlist)
+
+        m = auth_token.AuthProtocol(_middleware, self.conf)
+
+        env = {'REQUEST_METHOD': 'GET',
+               'HTTP_X_AUTH_TOKEN': self.token_dict['uuid_token_default']}
+
+        r = m(env, _start_response)
+        self.assertEqual(text, r)
+
 
 class V2CertDownloadMiddlewareTest(BaseAuthTokenMiddlewareTest,
                                    testresources.ResourcedTestCase):