Thanks a lot!
I did not see this. The expert tab is on the far right 
OK, but what sill puzzles me, the user still logs in with "cornelius" and internally it is mapped to the UUID.
The UUID is the "internal user".
So what is the loginname "cornelius" called?
This might result in a problem with the 2FA API, which gets the parameter IUser $user.
Usually the 2FA provider would use
$user->getUID()to pass the loginname to the auth system. Because the auth system also handles login names.
Looking at private/User/Account.php I do not see, which attribute or member function would return actually the login name of the user.
If you or @deepdiver1975 could shed some light how to retrieve the login name from the IUser object, this would be great!