Where does Briefcase look for its list of users to share folders with?

The Briefcase references the authentication system for those institutions using LDAP or a similar solution.  For institutions which rely only on the portal itself for authentication, the list of portal users maintained in the database is used.  With both implementations the briefcase can only recognize Portal users to enable folder sharing. 

In other words, folders can only be shared with users registered within the Portal (who have logged in at least once) or with previously defined uPortal groups.