/**
  * gets security token string from get, post or auth header
  * @return string
  */
 public static function getTokenStringFromRequest()
 {
     if (self::$rawToken) {
         return self::$rawToken;
     }
     $headers = OAuthUtil::get_headers();
     self::$rawToken = isset($_GET['st']) ? $_GET['st'] : (isset($_POST['st']) ? $_POST['st'] : (isset($headers['Authorization']) ? self::parseAuthorization($headers['Authorization']) : ''));
     return self::$rawToken;
 }