Summary: Has enough positions to pass.
- 4, "Since it is a JWT, JSON strings MUST be represented in UTF-8. ": Is that a new requirement, or a statement of fact about an existing JWT requirement? - 5.2: I'm not sure all readers will understand the meaning of "feature phone". Also, WAP and 2G don't seem all that relevant in 2017. - 5.2.1, first sentence, "The URL MUST be HTTPS URL.": Is that redundant to the similar requirement in the previous section? That instance had an "unless" clause, but this one does not. --2nd paragraph: "... MUST have appropriate entropy for its lifetime." Can you offer discussion (or a reference) for what constitutes "appropriate entropy"? -- 3rd paragraph: Is it reasonable that one would know if TLS would offer adequate authentication at the time of the signing decision? - 5.2.3, 2nd paragraph: "SHOULD use a unique URI": Why not MUST? Would it ever be reasonable to not do this? - 6.1, 2nd paragraph: What if validation fails? - 13: Do you want this in the final RFC? If not, it would be wise to add a note to the RFC editor to that effect.
- intro: "attacks... have been identified." yells out for a reference - it'd be a good bit better if implementers could easily find details of some such attacks, so I hope you add some refs here. - section 3; WAP? Really? I'm surprised any WAP technology would still be in use, even on feature-phones. Do you really need this? - section 4: I think it will turn out to be an error to allow for mixing query parameters and protected parameters (in a Request Object) in a single request. Do you really need that level of flexibility? It'd be simpler and less likely to be attackable to insist that all parameters be in the Request Object if one is used. (See also section 11.2.1 below.) - section 10: Is there nothing to be said about the new indirection caused by the request_uri? I'd have thought there were some corner cases that'd warrant a mention, e.g. if some kind of deadlock or looping could happen, or if one client (in OAuth terms) could use a request_uri value as a way to attempt attacks (to be assisted by an innocent browser) against some resource owner. - section 11: thanks for that, it's good. - section 11: Saying that an ISO thing is "good to follow" is quite weak IMO. (And is that ISO spec accessible? Hmm... it seems that one needs to accept cookies to get it which is wonderfully ironic;-) If the authors have the energy, I'd suggest trying to find better guidance that's more publically available in a privacy-friendly manner. (Or just drop the ISO reference if 6973 is good enough.)
Should this document maybe update rfc6749?
Thank you for addressing my DISCUSS point. New nit: URN needs a reference to RFC 8141.