Hi Rob,
Sorry but internally mojoPortal uses its own siteUser obejct which must be reflected in the mp_Users database. Any authenticated user must have a corresponding row in this table no matter what kind of authentication is used, therefore we create one automatically upon successful authentication when using Windows auth or LDAP/AD over forms authentication.
Windows authentication only works on local networks and using IE, it cannot be used on the internet. LDAP/AD over forms auth is the only way to use existing windows accounts over the internet. For people to use Windows Auth from home they would have to be connected to your lan over a vpn.
But again in all cases mojoPortal needs a row in mp_Sites for each authenticated user.
Best,
Joe