You can make an external list call that would query an LDAP server and writes the returned string into a user-defined property, rather than using Authentication.GetUserGroups.
Another alternative is storing the result of Authentication.UserGroups into a different Property before overwriting it with the result of Authentication.GetUserGroups. After you got your special attribute restore the value from a user-defined property.
Thanks for the hint Andre.
I searched again the community and for help this article is also helpful. Re: MWG LDAP query
I configured it like this
and my LDAP Filter like this
So it is possible to import attributes like country,mail etc.
very cool. Thanks for letting us know it works :-)