Authentication where the user profiles live in the eXist-db?

I was hoping to use an Orbeon XForm for user registration with their user info winding up in eXist as xml.

With subsequent login authentication making use of that and restricting access to (other) Orbeon forms accordingly.

Going over the java authentication example (using Tomcat) with users living in that tomcat-users.xml file works fine.

But I'm not seeing anything able to draw user profile info from eXist.

Has anybody done this - any tips? :)

Otherwise can someone suggest an alternative - e.g. it seems overkill but I guess I could use a relational database *just* for the user profile info?  i.e. so I could configure and use a "JDBCRealm" for authentication?

(but so far I've been liking this new world/new idea of *only* XML no RDBMS!! :)

Thanks,

Darren