Never attempted that, but try this:
- (For yourself only, if you are kerberized, provided you can logon to your old account) in your account (/profile/account), under Social, Kerberos-spnego, click Connect.
- (For a few users, as admin, by hand) Under /admin/users/USERNAME_HERE/identities, update or add ldap and Kerberos identities. The Kerberos id must match the uPN AD field from the new AD, and is case-sensitive. Sysinternals AD Explorer is your friend.
- (For a larger org, mass-update) Craft a PSQL query to update the info in (2). I do not remember where these are in the DB, but you’ll find them. Restart gitlab after this update. But backup the DB first please, so I can sleep sound at night