cssd-back/app/Providers/AuthServiceProvider.php

<?php

namespace App\Providers;

use Illuminate\Foundation\Support\Providers\AuthServiceProvider as ServiceProvider;
use Laravel\Passport\Passport;

class AuthServiceProvider extends ServiceProvider
{
    /**
     * The policy mappings for the application.
     *
     * @var array
     */
    protected $policies = [
        'App\Models\MedicalCenter' => 'App\Policies\MedicalCenterPolicy',
        'App\Models\User' => 'App\Policies\UserPolicy',
        'App\Models\TestType' => 'App\Policies\TestTypePolicy',
        'App\Models\Item' => 'App\Policies\ItemPolicy',
        'App\Models\Transfer' => 'App\Policies\TransferPolicy',
    ];

    /**
     * Register any authentication / authorization services.
     *
     * @return void
     */
    public function boot()
    {
        $this->registerPolicies();
        Passport::enablePasswordGrant();
    }
}