public function boot()
 {
     $this->app[DingoAuth::class]->extend('oauth', function ($app) {
         $provider = new OAuth2($app['oauth2-server.authorizer']->getChecker());
         $provider->setUserResolver(function ($id) {
             Auth::loginUsingId($id);
             return User::findOrFail($id);
         });
         $provider->setClientResolver(function ($id) {
             //TODO: Logic to return a client by their ID.
         });
         return $provider;
     });
 }