code: public function boot()
      {
          // Here you may define how you wish users to be authenticated for your Lumen
          // application. The callback which receives the incoming request instance
          // should return either a User instance or null. You're free to obtain
          // the User instance via an API token or any other method necessary.
  
          $this->app['auth']->viaRequest('api', function ($request) {
              if ($request->input('api_token')) {
                  return User::where('api_token', $request->input('api_token'))->first();
              }
          });
      }
docs: Boot the authentication services for the application.
  
  @return void