cancel_url (OpenID::Server::CheckIDRequest)

    # File lib/openid/server.rb, line 804
          def cancel_url
            # Get the URL to cancel this request.
            #
            # Useful for creating a "Cancel" button on a web form so that
            # operation can be carried out directly without another trip
            # through the server.
            #
            # (Except you may want to make another trip through the
            # server so that it knows that the user did make a decision.)
            #
            # Returns a URL as a string.
            if !@return_to
              raise NoReturnToError
            end

            if @immediate
              raise ArgumentError.new("Cancel is not an appropriate response to " +
                                      "immediate mode requests.")
            end

            response = Message.new(@message.get_openid_namespace)
            response.set_arg(OPENID_NS, 'mode', 'cancel')
            return response.to_url(@return_to)
          end