public static function current()
    {
        $token = Request::header('X-Auth-Token', Input::get('X-Auth-Token'));

        if (static::$_current === null && $token) {
            static::$_current = static::where('token', $token)
                ->where('expire_at', '>=', Carbon::now())
                ->first();
        }

        return static::$_current;
    }