I was created one project with laravel 5.4 and custom authentication to one table of Dynamics NAV (2017) trough web services, these are the steps that I was make to do this:

• I was folow some steps As this article explains perfectly: CustomUserProvider.php 
  • • Modify config/auth.php:

          'providers' => [
              'users' => [
                  //'driver' => 'eloquent',
                  'driver' => 'customuserprovider',
                  'model' => App\User::class,
              ],
      
              // 'users' => [
              //     'driver' => 'database',
              //     'table' => 'users',
              // ],
          ],
      

    • but then Modify providers/AuthServiceProvider to use my own customuserprovider:

       <?php namespace App\Providers; use Illuminate\Support\Facades\Gate; use Illuminate\Foundation\Support\Providers\AuthServiceProvider as ServiceProvider; class AuthServiceProvider extends ServiceProvider { /** * The policy mappings for the application. * * @var array */ protected $policies = [ 'App\Model' => 'App\Policies\ModelPolicy',
          ];
      
          /**
           * Register any authentication / authorization services.
           *
           * @return void
           */
          public function boot()
          {
              $this->registerPolicies();
              // added to modify auth provider that's the trick
               \Illuminate\Support\Facades\Auth::provider('customuserprovider', function($app, array $config) {
              return new CustomUserProvider($app['hash'], $config['model']);
                  });
              //
          }
      }