Get validation error messages in Lumen & Dingo API project

Controller.php

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use Dingo\Api\Exception\ValidationHttpException;
use Laravel\Lumen\Routing\Controller as BaseController;

class Controller extends BaseController
{
    /**
     * Override validate method use dingo validation exception
     *
     * @param Request $request
     * @param array $rules
     * @param array $messages
     * @param array $customAttributes
     */
    public function validate(
        Request $request, 
        array $rules, 
        array $messages = [], 
        array $customAttributes = [])
    {
        $validator = $this->getValidationFactory()->make(
            $request->all(), 
            $rules, $messages, 
            $customAttributes
        );

        if ($validator->fails()) {
            throw new ValidationHttpException(
                $validator->errors()
            );
        }
    }
}

LoginApiController.php

<?php

use Illuminate\Http\Request;

class UserApiController extends Controller
{
    use Helpers;

    function login(Request $request)
    {
        // Validate request
        $this->validate($request, [
            'username' => 'required|min:3',
            'password' => 'required|min:3'
        ]);

        // ...
    }
}