controller.php

<?php

namespace App\Http\Controllers;

use App\User as UserModel;

class UserController extends Controller
{
    public function index()
    {
        $users = UserModel::all();
        $response = [];
        foreach($users as $user) {
            $roles = $user->roles()->pluck('name');
            $userArray = $user->toArray();
            $userArray['roles'] = $roles;
            $response[] = $userArray;
        }
        
        return response()->json($response);
    }
}