I tried athelia and Authentic, and it somehow was not what I was looking for, too much for my needs.

Then I tried tinyauth, which was too little (no User Management at all, users have to be defined in a text file or via Environment variables)

I am now using Voidauth and I am very happy with it. It does what I need perfectly and without a hassle. Which is: Users and Groups, invite links for new users, LDAP server and first of all, it is very easy to use.