An alternative is to look at Container level authentication. E.g.
Tomcat has an LDAP authentication Realm class that works with AD. Other app containers probably have similar options.
You set this up and then "secure" your jforum directory with Web.xml security constraints.
Then enable RemoteUserSSO support.
The advantage here is that the container level AD support has a lot more people using it and therefore a lot more documentation/options available.
[originally posted on jforum.net by monroe]