class Google::Auth::WebUserAuthorizer::CallbackApp

def self.call env
  request = Rack::Request.new env
  return_url = WebUserAuthorizer.handle_auth_callback_deferred request
  if return_url
    [REDIR_STATUS, { LOCATION_HEADER => return_url }, []]
  else
    [ERROR_STATUS, {}, ["No return URL is present in the request."]]
  end
end