Auth::user() returns null

I faced a situation where Auth::user() always returns null, it was because I was trying to get the User in a controller's constructor.

I realized that you can't access the authenticated user in your controller's constructor because the middleware has not run yet.

As an alternative, you can define a Closure based middleware directly in your controller's constructor.

namespace App\Http\Controllers;

use App\User;
use Illuminate\Support\Facades\Auth;
use App\Http\Controllers\Controller;

class ProjectController extends Controller
{
    protected $user;

    /**
     * Create a new controller instance.
     *
     * @return void
     */
    public function __construct()
    {
        $this->middleware(function ($request, $next) {

            $this->user = Auth::user();

            return $next($request);
        });
    }
}

Any route that uses Auth() must be encapsulated in the web middleware. You're close, just move your Route::group(['prefix' => 'admin'], ...) into the group above.

Route::group(['middleware' => 'web'], function () {

    Route::auth();

    Route::get('/', 'HomeController@index');

    // Moving here will ensure that sessions, csrf, etc. is included in all these routes
    Route::group(['prefix'=>'admin',  'middleware' => 'admin'], function(){
        Route::get('/', function(){
            return view('admin.index');
        });

        Route::get('/user', function(){
            return view('admin.user');
        });
    });
});

Define middleware in the constructer of your controller and it will do the trick here

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