Laravel 5.x. Login authentication with username or email.

LoginController.php

<?php
namespace App\Http\Controllers;
use Illuminate\Http\Request;
use App\Http\Controllers\Auth\AuthController;
use Illuminate\Auth\CreatesUserProviders;
class LoginController extends AuthController
{
    use CreatesUserProviders;
    protected $app;
    protected $provider;
    /**
     * Handle a login request to the application with username or email.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return \Illuminate\Http\Response
     */
    public function prelogin(Request $request)
    {
        $this->app = app();
        $this->provider = $this->createEloquentProvider(config('auth.providers.users'));
        // Authenticate with username or email.
        $this->username = filter_var($request->username, FILTER_VALIDATE_EMAIL) ? 'email' : 'username';
        $request->merge([$this->username => $request->input('username')]);
        $credentials = $request->only($this->username, 'password');
        if ($user = $this->provider->retrieveByCredentials($credentials)) {
            // You may also want to access the user modal.
            // if ($user->hasRole('')) {}
            return $this->login($request);
        }
        return $this->sendFailedLoginResponse($request);
    }
    /**
     * Overwrite parent method so the correct login username input field has the
     * error message. Otherwise, failed login message may not appear.
     */
    protected function sendFailedLoginResponse(Request $request)
    {
        $this->username = 'username';
        return parent::sendFailedLoginResponse($request);
    }
}

routes.php

Route::auth();

// Place this below Route::auth() to override post login.
Route::post('login', 'LoginController@prelogin');