Thank you for your advices @jive!
Option #2 might be a good workaround for us.
[Geoserver-users] Disable / alter Geoserver web admin interface for external users - GeoServer / GeoServer User - OSGeo Discourse
[Geoserver-users] restrict access to the web administration interface - GeoServer / GeoServer User - OSGeo Discourse
security - Restrict access to geoserver’s web administration interface - Geographic Information Systems Stack Exchange