Shibboleth setup failure Error -- failed to map user ()

I did setup Shibboleth for the first time. Failing with “Error – failed to map user ()” Usually we do not login with email but with username and password. For some reason it cannot map users. Any Pointers will be helpful.

Shibboleth should be returning the username. With other OIDC systems we use the attribute preffered_name. It appears that whatever Shibboleth is returning as the REMOTE_USER is an empty string, which obviously we cannot map.

What’s your user_map_match or similar ood_portal.yml configurations?