public static function token()
    {
        $token = null;

        if (self::has('server.HTTP_X_TOKEN')) {
            $token = self::get('server.HTTP_X_TOKEN', 'md5');
        }

        if (self::has('request._token')) {
            $token = self::get('request._token', 'md5');
        }

        return $token;
    }