protected function getCurrentUrl() {
    $protocol = isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on'
      ? 'https://'
      : 'http://';
    $currentUrl = $protocol . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];
    $parts = parse_url($currentUrl);

    // drop known fb params
    $query = '';
    if (!empty($parts['query'])) {
      $params = array();
      parse_str($parts['query'], $params);
      foreach(self::$DROP_QUERY_PARAMS as $key) {
        unset($params[$key]);
      }
      if (!empty($params)) {
        $query = '?' . http_build_query($params, null, '&');
      }
    }

    // use port if non default
    $port =
      isset($parts['port']) &&
      (($protocol === 'http://' && $parts['port'] !== 80) ||
       ($protocol === 'https://' && $parts['port'] !== 443))
      ? ':' . $parts['port'] : '';

    // rebuild
    return $protocol . $parts['host'] . $port . $parts['path'] . $query;
  }