Allow login using username or email in Laravel 5.4

AuthController.php

<?php

namespace App\Http\Controllers\Auth;

use Illuminate\Http\Request;
use App\Http\Controllers\Controller;
use Illuminate\Foundation\Auth\AuthenticatesUsers;

class AuthController extends Controller
{
    use AuthenticatesUsers;

    /**
     * Get the login username to be used by the controller.
     *
     * @return string
     */
    public function username()
    {   
        if (filter_var(request('username'), FILTER_VALIDATE_EMAIL)) {
            request()->request->add(['email' => request('username')]);
            return 'email';
        }
        return 'username';
    }
}