Hard provisioning: de-provisioning should be supported

[thlehmann-ionos]

Although not documented, the user_oidc addon apparently supports hard user provisioning.

However, there's only a method to provision users, not to un-provision them.

Why is hard-provisioning in user_oidc used?

Because it implements IPasswordConfirmationBackend, which allows declaring that the user can not confirm the password. This is required for some functionalities in the settings, i.e. adding an app password.

If this backend was not used, the user would be asked to confirm these actions with a password (a Nextcloud backed user) the user does not have.

Expected

• Un-provisioning should be implemented.
• How to provision and un-provision should be documented.