Sync LDAP Groups using Kerberos

Hi, i’ve just got my xwiki up and running. The next step was using LDAP for checking the user credentials against the active directory and syncing some groups, which also worked successfully.

Now i try to switch to Kerberos login. The standard Kerberos login is already working, any previous logged in user can now. But how do get the AD/LDAP groups synced?
As far as i understood i have to create a new authclass using the java code of: https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Authentication/#HKerberosSSOAuthentication
But where should i put this code? Do i have to modify the content of the jar-files?
Anything else i have to take care of?

Thanks in advance,
Gerd

Or - is there a way to start the LDAP group mapping manually / by scheduler, even if authlass is set to AppServerTrustedKerberosAuthServiceImpl login and not to XWikiLDAPAuthServiceImpl?