Currently - it’s possible, but not so easy to install, since we don’t ship auth_ldap python package in mainstream package. You need to install it alongside the package. The good part is - we plan to change this, to include it in one ralph distribution.
If you’re willing to configure it anyway, there is description on the main gitter channel
and there is technical tutorial here: https://ralph-ng.readthedocs.io/en/stable/installation/configuration/.