Authenticate a user against multiple different backends
Currently, a single user can only be authenticated against a single backend. If a user exists in multiple backend with the same username, you get all sorts of funny reactions.
In the documentation about Dynamic Group Membership the described logic would make this possible. However, it doesn't work as described; Users end up in the wrong backend group and some UTM services throw authentication failure errors while the backend in question can successfully authenticate the user.
Please make it work as described in the documentation!