protected function errorResponse()
    {
        if(!empty($this->data['openid_return_to'])) {
            $response = array(
            'openid.mode'  => 'error',
            'openid.error' => 'Invalid request'
            );
            $this->redirect($this->response($response));
        } else {
            header('HTTP/1.1 400 Bad Request');
            $response = array(
                'ns' => $this->ns,
                'error' => 'Invalid request'
                );
            echo $this->keyValueForm($response);
        }
        die();
    }