Laravel authentication & authorisation with REMOTE_USER

I've got the following setup:

Apache Server 2.4.x which uses Kerberos for SSO Laravel 5.5 PHP 7.x MSSQL Database 12 with existing database structure, Usertable can be customized

In my Laravel application a user can access the application only if he/she already passed the apache login which means i can retrieve the REMOTE_USER variable from the server with

$user = $_SERVER['REMOTE_USER'];

What i intend to do is to use the Laravel authentication and authorisation for the rest of the application. I've looked into a lot of examples but found nothing which really suits.

Can anybody give a hint how to authenticate the $user in Laravel when accessing the application to get the credentials?

via Chebli Mohamed