Tomcat authenticates with Realms. These are nothing more than a class that will return a Principal object that contains a username, password and list of roles.
For QuickPlace there are no roles as such but there is ACL level. So, I mapped the role to the ACL entry (manager, author, reader). This will allow admins to extend QuickPlace into the J2EE world without needing to creating yet another directory.
To me, one of the really nice parts of QuickPlace is the user management. Adding, removing, editing users is really well thought out and it would be silly to have to re-work that with some complicated LDAP setup when you can use the domino backed classes to hook into the QuickPlace contacts1.nsf.
It is now up and published under GPL and hope it helps people extend QuickPlace functionality with Tomcat.
QuickPlace Realm for Tomcat