Detailed explanation of front-end and back-end login in Laravel 5.5 based on the built-in Auth module

php artisan make:auth

'guards' => [
 //...
 'admin' => [
  'driver' => 'session',
  'provider' => 'users',
 ],
 //...
 ],

class AdminController extends BaseController
{
 use AuthorizesRequests, DispatchesJobs, ValidatesRequests;

 public function __construct()
 {
 $this->middleware('auth:admin');
 }
}

<?php
namespace App\Http\Controllers\Admin;
use App\Http\Controllers\Controller;
use Illuminate\Support\Facades\Auth;
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;
 /**
 * Where to redirect users after login.
 *
 * @var string
 */
 protected $redirectTo = &#39;/admin&#39;;
 /**
 * Create a new controller instance.
 *
 * @return void
 */
 public function __construct()
 {
 $this->middleware(&#39;guest:admin&#39;)->except(&#39;logout&#39;);
 }
 /**
 * 重写登陆页面
 * @return \Illuminate\Contracts\View\Factory|\Illuminate\View\View
 */
 public function showLoginForm()
 {
 return view(&#39;backend.login&#39;);
 }
 /**
 * 重写退出方法
 * @param Request $request
 * @return \Illuminate\Http\RedirectResponse|\Illuminate\Routing\Redirector
 */
 public function logout(Request $request)
 {
 $this->guard()->logout();
 $request->session()->flush();
 $request->session()->regenerate();
 return redirect(&#39;/admin/login&#39;);
 }
 /**
 * 重写guard认证
 * @return mixed
 */
 protected function guard()
 {
 return Auth::guard(&#39;admin&#39;);
 }
}

public function handle($request, Closure $next, $guard = null)
{
 if (Auth::guard($guard)->check()) {
  $path = $guard ? '/admin' : '/home';
  return redirect($path);
 }
 return $next($request);
}

/**
 * 重写实现未认证用户跳转至相应登陆页
 * @param \Illuminate\Http\Request $request
 * @param AuthenticationException $exception
 * @return \Illuminate\Http\JsonResponse|\Illuminate\Http\RedirectResponse
 */
 protected function unauthenticated($request, AuthenticationException $exception)
 {
 if($request->expectsJson()){
  return response()->json(['message' => $exception->getMessage()], 401);
 }else{
  return in_array('admin', $exception->guards()) ? return redirect()->guest('/admin/login') : redirect()->guest('login');
 }
 }