Is your feature request related to a problem? Please describe.

The Upgrade notes for SimpleSAMLphp 2.3 fail to mention a breaking change:

• The auth.adminpassword configuration value no longer allows raw passwords (see FAQ).

This caused admins being locked out after upgrade. I don't remember having seen any prior warning about this.

Describe the solution you'd like
Describe this breaking change in the Upgrade notes.

Describe alternatives you've considered
Allow raw passwords again, but as a deprecated feature. And warn users/admins if raw passwords are used.

Additional context
Screenshot of surprise waiting admins who wish to login after upgrade: