How does laravel-adldap2 determine a user match with local user table

Question

Laravel 6. CentOS 7

I have an existing user table that was used with standard Laravel Auth. I've converted to LDAP but if a user logs in, the system tries to create a new user rather than syncing the existing entry unless there is an objectguid. This fails of course because of duplicate constraints.

I have another app that I'm doing the same thing and it seems to be working as expected. I cant figure out what's different on the configurations outside of some column names are different so the sync config looks a little different.

How does ldap2 determine a match in the local table before creating a new one?

Thanks