Allowed username both with domain (@domain.com)-part and without, LDAP windows AD

[t-aleksander]

Converted from discussion: #3060

Hello.
Ive set up Defguard with LDAP connection to my AD, and it works fine. However it will only allow log in using username without domain part. How should i set it up to allow the domain part as well?
I.e.
user@domain.com <- Not allowed
user <- Allowed

The current Username attribute used is: sAMAccountName, and i would like to allow userPrincipalName as well.