AutoCreate with Group Membership

We are running 4.0.2 with external authentication to LDAP and would like to auto create privileged users with membership to a specific group. I can see that by setting

Set($AutoCreate, {Privileged => 1});

You can update the privileged attribute in their profile but this does not seem to be working and I cannot find documentation for automatically adding them to a group. Is this even possible?

We are running 4.0.2 with external authentication to LDAP and would like to auto create
privileged users with membership to a specific group. I can see that by setting

RT-Authen-ExternalAuth or WebExternalAuth

Set($AutoCreate, {Privileged => 1});

These settings applied when logging into the web ui for the first time
and being autocreated by either of the methods above.

You can update the privileged attribute in their profile but this does not seem to be working
and I cannot find documentation for automatically adding them to a group. Is this even
possible?

Neither of the external auth solutions support auto-adding to a group.

-kevin