public String getUsernameField() {
        return usernameField;
    }
Returns the LDAP field name that the lookup for an authorization identity (username to act as) will be performed
on. By default, this is "uid".

@return the LDAP field that the authorization identity (username to act as) lookup will be performed on.
xmppserver/src/main/java/org/jivesoftware/openfire/ldap/LdapManager.java