This option gives us
- flexible authentication options where the name used for logging on
does not have to be the account name
e.g. use ldap_filter = (&(obhjectclass=inetOrgperson)(|(cn={0]})(mail={0})))
to allow loginng on using the cn or the mail address
- automatically consistent / canonicalized username values
(i.e. exactly the way the LDAP server returns them)