Laravel 5.6让用户遇到路由问题

How to get an id of the user?

app/routes/web.php

Route::group(['middleware' => 'auth'], function()
{
    var_dump(Auth::user());
}

It returns null.

Simple things made difficult.. Also there is no reliable explanation

How to handle this?

You have not defined any route, try this instead:

Route::group(['middleware' => 'auth'], function () {
    Route::get('/', function () {
        dd(Auth::user());
    });
});

Change the '/' to what ever you like, does that work for you?