NoBrainerQuiz / web

app/Http/Controllers/Auth/LoginController.php

<?php

namespace App\Http\Controllers\Auth;

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

class LoginController extends Controller
{
    /*
    |--------------------------------------------------------------------------
    | Login Controller
    |--------------------------------------------------------------------------
    |
    | This controller handles authenticating users for the application and
    | redirecting them to your home screen. The controller uses a trait
    | to conveniently provide its functionality to your applications.
    |
    */

    use AuthenticatesUsers;

The trait Illuminate\Foundation\Auth\AuthenticatesUsers requires some properties which are not provided by App\Http\Controllers\Auth\LoginController: $maxAttempts, $decayMinutes

    /**
     * Where to redirect users after login.
     *
     * @var string
     */
    protected $redirectTo = '/host/dashboard';

    /**
     * Create a new controller instance.
     *
     * @return void
     */
    public function __construct()
    {
        $this->middleware('guest')->except('logout');
    }

    protected function credentials(Request $request) 
    {
        $field = filter_var($request->get($this->username()), FILTER_VALIDATE_EMAIL) ? $this->username() : 'username';

        return [
            $field     => $request->get($this->username()),
            'password' => $request->password
        ];
    }

    public function logout(Request $request)
    {
        $user = Auth::user();
        $this->guard()->logout();
        $request->session()->invalidate();
        return redirect()->route('login')->with('logoutMessage', 'You have been successfully logged out ' . $user->username);

Accessing username on the interface Illuminate\Contracts\Auth\Authenticatable suggest that you code against a concrete implementation. How about adding an instanceof check?

    }

    public function showLoginForm()
    {
        return view('quiz_host.auth.login');
    }
}