public static function getRoleIdByAppIdAndUserId($app_id, $user_id)
    {
        $cacheKey = static::makeRoleIdCacheKey($app_id, $user_id);
        $result = \Cache::remember($cacheKey, \Config::get('df.default_cache_ttl'),
            function () use ($app_id, $user_id) {
                try {
                    return static::whereAppId($app_id)->whereUserId($user_id)->value('role_id');
                } catch (ModelNotFoundException $ex) {
                    return null;
                }
            });

        return $result;
    }