public function getAuthorizeUrl($request_token, $callback_uri = NULL, $state = NULL) {
    $request_token = array(
      'oauth_token' => is_array($request_token) ? $request_token['oauth_token'] : $request_token,
    );
    // authorize
    $url = Url::factory($this->getConfig('base_url'));
    $url->addPath($this->getConfig('authorize_path'));
    $url->setQuery($request_token);
    return (string)$url;
  }