Just a small hint as it seems that oC 9+ contains yet another hidden feature which is not documented (as quite often):
Always wondering what the following command is used for:
The docs itself about it is not really descriptive:
Synchronizes users to the system addressbook
However the documentation for this and the usage is completely missing. It seems one can attach an external CardDAV client to:
and is getting the users existing in the ownCloud installations as Contacts / VCARDs.
You can even sync these addressbooks over federated Clouds with oC 9: https://github.com/owncloud/core/pull/20948
Ref for a request to document this: