How to promote user to admin

I’d like to promote an user to admin. User is imported from ldap (testrealm).

What is the best practice to accomplish this task?

I’ve tried with pi-manage, but this method will end up creating a new, local user. Is it even possible to promote users from external providers to act as admin?

“administrative realms”.

Not a single user but the complete realm will get administrative rights. Check your “admin” policies!