In laravel\passport install into lumen article can not find CheckClientCredentials file ?

Hello,

I follow https://medium.com/the-andela-way/setting-up-oauth-in-lumen-using-laravel-passport-2de9d007e0b0 to install laravel\passport into lumen project, but reading it with :

$app->routeMiddleware([
  'auth' => App\Http\Middleware\Authenticate::class,
  'client' => \Laravel\Passport\Http\Middleware\CheckClientCredentials::class,

I did not find file CheckClientCredentials , I suppose it must be located at /app/Http/Middleware subdirectory. In the article there is a link at https://gist.github.com/DavidNgugi/657544d36bd1bc1cb1b89fd63d8fd59c

But I also did not find content ofthis file. Which content must it have?

If the way in the article valid and must work ?

Thanks!