Kerberos authentication not working with Apache and PHP-FPM

Question

I have configured kerberos authentication in apache with a php-fpm drupal backend.

Checking the apache logs it looks fine at first glance but somehow it seems that the authenticated user gets lost somewhere.

The Drupal Watchdog Logs say:

Does this try to hint that the php-fpm process does not get the $_Server[Remote_User] Variable? Does Apache mod_auth_kerb authenticate the user while php doesn't? Could I pass that server envar to php-fpm somehow?

Answer 1

Okay if fixed this by simply adding a print_r($_SERVER) for debugging in an index.php and disabling drupal.
It turns out that the correct Variable is $_SERVER[Redirected_Remote_USER] maybe because of php-fpm.

As the Drupal LDAP SSO Module even has field with a help text beneath telling "...or either Redirect_Remote_User" it was easy to fix it after debugging.