not an authentik user, but after skimming their docs i think you have to:

1. create a role “ocisAdmin” via authentiks admin interface
2. give this role to a group in the admin interface or create one.
3. assign a user thats supposed to be an owncloud admin to the group

it might be that you also have to define somekind of mapper to include this in the informations owncloud receives from authentik, but as i said i only skimmed the docs and would personally just try it without the mapper.

oh, thats good to know, forgejo seems way nicer for self hosting than the limited gitlab open source core.

https://distribution.github.io/distribution/

is an opensource implementation of a registry.

you could also self host something like gitlab, which bundles this or sonatype nexus which can serve as a repository for several kinds of artifacts including container images.