More detailed login failures on linelog

[R3DNano]

I have been playing around with linelog in order to send all the status via
rsyslog to a remote machine and it has been working pretty well.
What I still don't manage to get is how to have more detailed
authentication failure messages in order to troubleshoot what went wrong.
I'm currently using %{Module-Failure-Message}, but i only get stuff like
"EAP module failure" instead of something more useful like "username is not
found in ldap" or "Password incorrect"
How can I do this?

Thanks!