Did I mentioned that the config parser for JAAS is one of the worst in
dealing with errors ? For some reason I didn't quote the option - it was
a simple pathname - and all I got was "Can't find configuration file".

Next error was tomcat's fault - it seems the memory ( i.e.
tomcat-user.xml) module is broken ( class cast errors ) and not completely
implemented.

I'll try to fix it - but if nobody is willing to help I'll probably just
give up...

After a while I got the MemoryLoginModule to (kind of ) work - now the whole user/role principal configuration in JAASRealm needs a bit of magic and I need to insert the RolePrinciplas.