Change invocation of call to keystone middleware for token validation

that meets Mitaka expectations.

Change-Id: I98bfcec13eba314504c81c45f927cee36f0d5234
Closes-Bug: 1608815

src/config/api-server/vnc_auth_keystone.py

@@ -224,7 +224,11 @@ def verify_signed_token(self, user_token):
     def token_valid(self, env, start_response):
         status = env.get('HTTP_X_IDENTITY_STATUS')
         token_info = env.get('keystone.token_info')
-        return token_info if status != 'Invalid' else None
+        start_response('200 OK', [('Content-type', 'text/plain')])
+        return token_info if status != 'Invalid' else ''
+
+    def start_response(self, status, headers):
+        pass
 
     def validate_user_token(self, request):
         # following config forces keystone middleware to always return the result
@@ -233,6 +237,6 @@ def validate_user_token(self, request):
         conf_info['delay_auth_decision'] = True
 
         auth_middleware = auth_token.AuthProtocol(self.token_valid, conf_info)
-        return auth_middleware(request.headers.environ, None)
+        return auth_middleware(request.headers.environ, self.start_response)
 
 # end class AuthService