[OAUTH-WG] DPoP followup II: confirmation style

[Brian Campbell <[e-mail]>]

There were a few items discussed somewhat during the recent interim
<https://datatracker.ietf.org/meeting/interim-2020-oauth-16/session/oauth>
that I committed to bringing back to the list. The slide below (also
available with some typos and omitted words as slide #18 from the interim
presentation
<https://datatracker.ietf.org/meeting/interim-2020-oauth-16/materials/slides-interim-2020-oauth-16-sessa-dpop-01.pdf>)
is the second one. To summarize (by basically repeating the content of the
slide): It’s been suggested that, for resource access, having the JWK in
the header of the DPoP proof JWT makes it too easy to just use that key to
validate the signature and miss checking the binding to the AT’s cnf/jkt
hash, which undermines the value of doing the binding in the first place.
As I see it, there are two options here and I'd like to gauge WG consensus
on which to move forward with.

   1. It’s fine as is (AS/RS symmetry is nice, it's the same way
   confirmation works in MTLS/TB, and the binding check is kinda fundamental
   to the whole thing so it's not unreasonable to expect implementers to do it)
   2. For resource access, put the full JWK in the AT’s confirmation and
   omit it from the proof (less error prone, no hash function needed for
   confirmation, somewhat less data overall between the two artifacts)



[image: Slide18.jpg]

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