[art] Artart last call review of draft-ietf-oauth-step-up-authn-challenge-12

[Robert Sparks via Datatracker <[e-mail]>]

Reviewer: Robert Sparks
Review result: Ready with Issues

Summary: essentially ready but with issues to consider before being published
as a proposed standard RFC.

Issues:

I expected to find some discussion of considerations of avoiding "step down"
given the intuitive appeal to "step up". Can the client or Authorization server
notice if the resource server has through whatever fault asserted that it will
only accept the use of an authentication context class that is blatantly
inferior to what has already been provided? And if they notice, what is
expected to happen? Or is it expected that this is allowed, particularly when a
short max_age is also supplied?

The document also suggests that the client hold on to, and possibly re-use in
the future, access tokens that have been challenged as having insufficient user
authorization. Is this behavior something that follows a well-known and
well-implemented pattern documented elsewhere? If so, a pointer would be
useful. If not, this seems like something that deserves more discussion if not
more definition.

Nits:
The reference to abr-twitter-reply will go away with the changelog when the RFC
Editor removes it. It would be kind to acknowledge that in the note to the RFC
Editor so that they know it's expected and don't have to ask.