The jump address should be modified in the middleware

Authenticate under AppHttpMiddleware
return redirect()->guest('admin/login');
That’s it

Authenticate middleware

public function handle($request, Closure $next, $guard = null)
    {
        if (Auth::guard($guard)->guest()) {
            if ($request->ajax()) {
                return response('Unauthorized.', 401);
            } else {
                return redirect()->guest($guard.'/login'); //注意这里的$guard
            }
        }

        return $next($request);
    }

route.php

Route::group(['middleware' => ['auth:admin']], function () { // auth:admin 调用auth中间件的时候传递一个admin，这个admin正好是被中间件的$guard接收，于是访问后台的时候都会被跳转导admin/login，同理 前台用户登陆的中间件可以是 auth:user , 这样会跳转到user/login

        Route::get('admin/index', 'AdminController@index');
    });