microservice-api-gateway/app/Providers/AuthServiceProvider.php

<?php

declare(strict_types = 1);

namespace App\Providers;

use Dusterio\LumenPassport\LumenPassport;
use Illuminate\Support\ServiceProvider;

class AuthServiceProvider extends ServiceProvider
{
    /**
     * Register any application services.
     *
     * @return void
     */
    public function register()
    {
    }

    /**
     * Boot the authentication services for the application.
     * If you desire to handle the request via simple mechanism
     * $this->app['auth']->viaRequest('api', function ($request) {
     *      if ($request->input('api_token')) {
     *               return User::where('api_token', $request->input('api_token'))->first();
     *      }
     *  });
     *
     * @return void
     */
    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.

        LumenPassport::routes($this->app->router);
    }
}