public static function retrievePT($target_service, & $err_code, & $err_msg)
    {
        phpCAS::_validateProxyExists();

        try {
            return (self::$_PHPCAS_CLIENT->retrievePT($target_service, $err_code, $err_msg));
        } catch (Exception $e) {
            phpCAS :: error(get_class($e) . ': ' . $e->getMessage());
        }
    }