The OAuth 2.0 Authorization Framework: JWT-Secured Authorization Request (JAR)
draft-ietf-oauth-jwsreq-34

The directorate reviews are from 15 or more versions ago.  I wonder if returning documents like this should be sent through the directorates again as matter of course.

Abstract: "... the communication through the user agents are not ..." -- s/are/is/

Section 1 expressly cites two IANA URLs.  I suggest simply naming the registry or sub-registry; the URLs might not be permanent.  Or if you like the URL, do it as a reference, as you did with [IANA.MediaType].

The two bullets at the end of Section 1 toggle between "crypto" and "cryptography".  I suggest picking one, preferably the latter (as did the rest of the document).

In Section 3, should URI and URL include references to their defining RFCs?  I realize a reader familiar with this space probably knows those terms, but they seem to be the only acronyms without a reference here.

When would an implementer legitimately disregard the SHOULD in Section 4?

As Benjamin Kaduk also expressed, I'm a little puzzled by this text in Section 5.2: "The "request_uri" value MUST be reachable by the Authorization Server."  Is this part of the protocol?

All of the subsections of Section 9 say: "This specification adds the following values to the "OAuth Parameters" registry established ..." but they all are actually modifying different sub-registries.  I suggest naming the sub-registries explicitly.  I realize the subsection titles have it right, but this line of repeated prose had me squinting a bit.

"NoObj" in the "I read the protocol action, and I trust the sponsoring AD so have no problem and / or this is outside my area of expertise or have no cycles" sense of the term.
I'm largely relying on the  fact that the previous Ops&Mgmt AD's, Kathleen, Jari, Ben, et al balloted Yes or NoObj.

Thank you for the work put into this document. 

Please find below a couple of non-blocking COMMENTs.

I hope that this helps to improve the document,

Regards,

-éric

== COMMENTS ==
Should the document shepherd's write-up be updated ? It is dated October 2016... about 4 years ago.

-- Section 5.2 --
Based on the long history of this document, is the following statement "Many phones in the market as of this writing still"  still valid ?

-- Section 5.2.1 --
Suggest to give a hint about the use of tfp.example.org (TFP is expanded only in section 10.2).

== NITS ==

Please check the ID-NITS at https://tools.ietf.org/idnits?url=https://tools.ietf.org/id/draft-ietf-oauth-jwsreq-26.txt

Thank you for addressing my DISCUSS point.

New nit: URN needs a reference to RFC 8141.

[updating again to link to https://mailarchive.ietf.org/arch/msg/oauth/POfiIMFXpUQTl5nPvgb7YDcLkE0/
to note that my first update kind of missed the point.]
[updated to note that, per https://mailarchive.ietf.org/arch/msg/oauth/Lqu15MJikyZrXZo5qsTPK2o0eaE/
and the JWT BCP (RFC 8725), some discussion of why explicit typing is not used would be in order]

Thanks for the many updates as we worked through the issues.

Let's also add a note about "whose JWT Claims Set holds the JSON encoded
OAuth 2.0 authorization request parameters" to the definition of Request
Object in Section 2.1 (in addition to the note in the Introduction); my
apologies for not including that when I suggested the change to the
Introduction.

Please update the Content-Length in the example in Section 5.2.3.


Section 4

   The client determines the algorithms used to sign and encrypt request
   objects.  This decision can be based on metadata the client
   registered via dynamic client registration [RFC7591] using the
   parameters "request_object_signing_alg",
   "request_object_encryption_alg", "request_object_encryption_enc" as
   defined in the the IANA "OAuth Dynamic Client Registration Metadata"
   registry [IANA.OAuth.Parameters] established by [RFC7591].

I had to read this ("this decision can be based on [...]") a few times
to understand it.  If I understand correctly, the idea is that the
client will register with the AS the keys it will use for constructing
the JAR, and in that way the AS has a binding from JAR-signing key to
the specific client and request.  So it's true that the decision of what
key to use "can be based on" the metadata that the client registered, in
that deciding to use a different key than the registered one(s) is
likely to cause the AS to reject the request, but that's perhaps not the
main point.  Would it work to instead just say that "The keys used to
sign and encrypt request objects (and thus, the algorithms that can be
used with those keys) can be registered via dynamic client registration
[...]"?

Section 5.2

   The contents of the resource referenced by the URI MUST be a Request
   Object, unless the URI was provided to the client by the
   Authorization Server.  The "request_uri" value MUST be either URN as
   defined in RFC8141 [RFC8141] or "https" URI, as defined in 2.7.2 of
   RFC7230 [RFC7230] .  The "request_uri" value MUST be reachable by the
   Authorization Server.

I defer to my ART-area colleagues, but I'm not sure what it means for a
URN URI to be "reachable"; is this requirement intended to only apply to
the "https:" case?

Section 5.2.1

   It is possible for the Request Object to include values that are to
   be revealed only to the Authorization Server.  As such, the
   "request_uri" MUST have appropriate entropy for its lifetime.  For

Is there a good reference for what the lifetime of such a request might
be?  Perhaps I've been reading too much of GNAP, but my intuition is
that much of the time these requests will be single-use, and I don't
have as clear of a picture for when they might persist longer.  There
are also potential security considerations for long-lived request
objects, in terms of making sure that there is a binding between the
client's intent to use a given request object for a given request, the
user's authorization, etc.

Section 5.2.3

(side note) I'd consider updating the timestamps in the example response
(and perhaps moving to Apache 2.4+ as well?).

Section 6.x

(nit) I suggest consistency in subsection headings, so, e.g., "JWE
Encrypted Request Object" and "JWS Signed Request Object".

Section 6.2

   The Authorization Server MUST perform the signature validation of the
   JSON Web Signature [RFC7515] signed request object.  For this, the
   "alg" Header Parameter in its JOSE Header MUST match the value of the
   pre-registered algorithm.  The signature MUST be validated against
   the appropriate key for that "client_id" and algorithm.

This text suggests that pre-registration is mandatory, whereas up in
Section 4 the client's choice of algorithm was merely something that
"can be based on [metadata registered via dynamic registration]".  I
know that dynamic registration is not the only kind of registration
possible, but we may want to wordsmith one (or both) location to improve
the consistency.

Section 6.3

I'd suggest reiterating here the requirement to verify "client_id"
consistency between Request Object and request parameters.

Section 10

I'd consider reiterating the security importance (i.e., what breaks if
you don't apply the check) of a few key compliance requirements and
which entity is responsible for enforcing them:

- the "request" and "request_uri" parameters MUST NOT be included in
  request objects, from Section 4

- The request object has the mime-type
  "application/oauth.authz.req+jwt", also from Section 4

- The client_id in the request object has to match the client_id from
  the request query parameters, from Section 5

- The AS must only use parameters from the request object, even if the
  client has duplicated them in the query parameters, also from Section 5

Section 10.2

   (e)  When a third party, such as a Trust Framework Provider(TFP),
        provides an endpoint that provides a Request Object URI in
        exchange for a Request Object.  The same requirements as (b) and
        (c) above apply.  In addition, the Authorization Server MUST

The (b) case is "the symmetric key for JWE encryption"; do we mean "(c)
and (d)" here?

Section 10.3

I'm not sure whether the key point of this section is "the following
endpoints are RECOMMENDED [...] to use this practice" or "an extension
specification should be created as a measure to address the risk".  That
is, can a deployment unilaterally apply the message-position and
intended-interaction-endpoint protections now, or is there need for
additional specification work first?

Section 10.4

I'm not sure how much of this is distinct from the Request URI Rewrite
discussed in Section 10.4.2, but having the request object contents be
in a separately dereferenceable URI introduces risk of the dereferenced
Request Object being dissociated from the triggering request.  (This
could happen due to internal error on the client or service hosting the
requested URI or content skew over time, in addition to a request URI
rewrite.)  Having an externally provided single-use nonce in the reqest
object would provide a mitigation, but it also (if I understand
correctly) not compatible with all of the envisioned use cases for JAR.

Section 10.5

Should the rejection of "alg":"none" be limited to the
require_signed_request_object case, or universally applied?

Section 12.1

   (2)  (Translation Process) The client uses the client credential that
        it got to push the request object to the TFP to get the
        "request_uri".

If I understand correctly, the TFP also verifies that the request object
is consistent with the claims the client is eligible for based on the
certification step in (1).

Section 12.2.2

   Therefore, per-user Request Object URI should be avoided.

If I understand correctly, the only possible alternative is to have
per-request URIs (right?), as coalescing multiple user's requests into a
single request object URI seems to pose several difficulties.  We could
perhaps make the recommended alternative more clear.

Should this document maybe update rfc6749?

Hi,

Only one minor comment:

I liked the reference to max URL size for older versions of Internet Explorer, but wonder if that is still really relevant in 2020?  Or perhaps it could now be removed?

Regards,
Rob

- 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.)