You could schedule a job to cleanup the authority.
As for expiration I don’t think there’s such a thing.
You could set them up with an alternate profile. You could set an expiration on the User ID to disable or delete after a specific date and time.
If you need assistance with the scheduled job option let us know what platform you’re running on.
DB2 I want to assume it’s AS400 but I’m not sure by your question’s tags.