Feature request: Allow accounts to be deactivated when the user is removed from an external auth provider

[TheLastProject]

Description:

Currently, I'm using Synapse together with mxisd as identity server (which uses LDAP as backend). It would be great if Synapse could occasionally check if the users still exist according to the identiy server, so that accounts can be automatically deactivated. A similar idea to https://docs.nextcloud.com/server/15/admin_manual/configuration_user/user_auth_ldap_cleanup.html, but then for identity servers in general instead of explicitly LDAP.

[richvdh]

I think this is a duplicate of #4158?

[TheLastProject]

Hmm, I'd like the account completely disabled/deleted so it also doesn't show up in the directory anymore, but it's at very least similar, yes.

[richvdh]

Ah right, yes.

There's more than one way to implement this, and I'm not sure a periodic callout to the identity server is the right one, since it would only work with mxisd setups. A more general solution is needed for external authentication providers in general.