first_name and last_name are gathered (currently) by space-splitting the 'cn' field. This is correct unless you don't have spaces in your 'cn' field at which point user creation fails.

I have switched to using displayName, but this is not a permanent fix. I might recommend something similar to LDAP_UID_MASK, but it is not likely as simple.

I tested this on my server by logging in with an unregistered user using the LDAP backend. The user creation was successful.