'WSGI application for handling the OAuth 2.0 redirect callback.
If you need finer grained control use `callback_handler` which returns
just the webapp.RequestHandler.
Returns:
A webapp.WSGIApplication that handles the redirect back from the
server during the OAuth 2.0 dance.'

def callback_application(self):

    return webapp.WSGIApplication([(self.callback_path, self.callback_handler())])
