Single sing on. Have a look at the option:
$Configuration['AUTHENTICATION_MODULE'] = 'People/People.Class.SingleSignOn.php';
in vanilla/conf/settings.php and appg/init_ajax.php which is where the default it. This tells vanilla which file to use to do authentication.
Then look at vanilla//library/People/People.Class.Authenticator.php which is the simple template. You can then copy this file to something else (those name goes into the option above) and edit that file to suite your needs.
Simple.
December 2009