Enable an additional lookup against an LDAP directory
during login and user creation to ensure that only
specific users can login and register on the EteBase
server instance.
This lets servers share a dashboard url with clients so that they in
turn can present clients with a settings dashboard.
We currently use it on the main server, but self-hosted servers may
also benefit from it for letting users manage some of their settings
(e.g. 2FA).