[Zope] Generic User Folder - custom user properties

I have (I hope) simple question : I use Generic User Folder for authentication of users against Postgress database. I rewrote the appropriate DTML methods, and it works. However, with the AUTHENTICATED_USER, I only get the name of user, its roles and domain. I need to associate another attribute/property, called 'user_id', which is an integer value of the user's record in the database. The value should then be used in subsequent SQL queries on behalf of the user. My question is, if it is possible (so that I can then call "AUTHENTICATED_USER.getProperty('user_id')") and at which point of Generic User Folder/authentication process I should assign the property value? Is there an easy way? Thanks, Michal Bukovjan