Protocols are referred to in the charter - we are trying to stall that for now, as people are jumping straight into protocol messages and data elements. Accounting requires an identity not just a authentication, distinct for tracking instances, and unauthenticated users. Also authorization by role. How this is provided is open for discussion. Some authentication methods may not allow non-repudiation.
Technical problems are difficult to satisfy.
Marcus suggests solving the obvious cases first. VoIP may involve billing requirements, and certainly inter-domain issues SIP AAA server can return users profile, which can include calling features, speed dial, etc. No, we don't want to go down rathole of distinguished names. But the design goal should include performance issues, if there are lots of iterations of authentications over the life of the individual sessions. Differences between flat-rate billing and usage sensitive or transactional billing used as example to demonstrate different requirements.