Re: [Ace] [EXTERNAL] Francesca Palombini's Discuss on draft-ietf-ace-oauth-authz-38: (with DISCUSS and COMMENT)

[Hannes Tschofenig <[e-mail]>]

Hi all,

what is the motivation for re-opening the discussion about this aspect? This was discussed in the working group before and we reached a conclusion about what we want to support.

The use of HTTP/JSON is extremely useful.

Ciao
Hannes

-----Original Message-----
From: Cigdem Sengul <[e-mail]>
Sent: Thursday, March 25, 2021 3:10 PM
To: Francesca Palombini <francesca.palombini=[e-mail]>
Cc: Seitz Ludwig <[e-mail]>; The IESG <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]
Subject: Re: [Ace] [EXTERNAL] Francesca Palombini's Discuss on draft-ietf-ace-oauth-authz-38: (with DISCUSS and COMMENT)

Hello,
I would like to add my two cents to this as the MQTT-TLS profile does use HTTP/JSON for client-AS and rs-AS communication as similar already was supported in MQTT implementations between an MQTT broker and external servers (e.g., via auth plug-ins).

For points like 13: Making CBOR mandatory would break how it is implemented for MQTT-TLS, which implements the AS creation hints as a User Property inside an MQTT message.
"The User Property is a UTF-8 string pair, composed of a name and a value.
The name of the User Property MUST be set to
   "ace_as_hint".  The value of the user property is a UTF-8 encoded
   JSON string containing the mandatory "AS" parameter, and the optional
   parameters "audience", "kid", "cnonce", and "scope" as defined in
   Section 5.1.2 of the ACE framework"

Kind regards,
--Cigdem



On Thu, Mar 25, 2021 at 1:53 PM Francesca Palombini <francesca.palombini= [e-mail]> wrote:

> Ludwig,
>
> Thank you for the quick reply, and for the useful background information.
>
> As I said, I think this document is important and should move forward
> asap, and it can do so without changing the main assumptions, with
> some additional clarifications in the text about CBOR vs "other" when
> HTTP is used (which in my opinions are necessary - see points 1, 8,
> 10, 11, 13, 15, 17, 22, 23, 26, 28).
>
> What I wanted to highlight is that it would simplify the document a
> lot to just remove this flexibility, for which I don't understand the
> motivation, and say "CBOR is mandatory" even when HTTP is used. The
> flexibility could be added in a future document if needed. However, I
> understand that there is history in the working group, and I will step
> back and remove my DISCUSS if I am in the rough. Note however that in
> terms of work on the document I suspect that keeping this flexibility will require more work, not less.
>
> Looking forward to discussing this with Ben during the telechat.
> Francesca
>
> On 25/03/2021, 08:50, "iesg on behalf of Seitz Ludwig" <
> [e-mail] on behalf of [e-mail]> wrote:
>
>     Hello Francesca,
>
>     Thank you for your review. I will address your detailed comments
> separately, with regards to your DISCUSS:
>
>     The option to allow both HTTP and JSON for any leg of the
> communication (client-AS, rs-AS, client-rs) was the result of long
> discussions in the WG. If I recall correctly the intent was to allow
> legacy OAuth 2.0 equipment (i.e. not supporting ACE) to be used in ACE
> interactions on those legs of the communication where no constrained
> devices are involved.
>     I am reluctant to reopen these discussions at this point in time,
> and I suspect doing the necessary analysis to provide in-depth
> considerations on the choices between HTTP/CoAP and JSON/CBOR will
> significantly delay the progress of this document.
>
>     @ace-chairs: What is your suggestion on how to best handle this?
>     (Please note that I am unable to commit significant amounts of
> time to this work in the foreseeable future)
>
>     Regards,
>
>     Ludwig
>
>
>     > -----Original Message-----
>     > From: Ace <[e-mail]> On Behalf Of Francesca
> Palombini via
>     > Datatracker
>     > Sent: den 24 mars 2021 15:50
>     > To: The IESG <[e-mail]>
>     > Cc: [e-mail]; [e-mail]; draft-ietf-ace-oauth-
>     > [e-mail]; [e-mail]
>     > Subject: [EXTERNAL] [Ace] Francesca Palombini's Discuss on
> draft-ietf-ace-
>     > oauth-authz-38: (with DISCUSS and COMMENT)
>     >
>     > Francesca Palombini has entered the following ballot position for
>     > draft-ietf-ace-oauth-authz-38: Discuss
>     >
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>     >
>     >
>     > Please refer to
> https://www.ietf.org/iesg/statement/discuss-criteria.html
>     > for more information about IESG DISCUSS and COMMENT positions.
>     >
>     >
>     > The document, along with other ballot positions, can be found here:
>     > https://datatracker.ietf.org/doc/draft-ietf-ace-oauth-authz/
>     >
>     >
>     >
>     >
> ----------------------------------------------------------------------
>     > DISCUSS:
>     >
> ----------------------------------------------------------------------
>     >
>     > Thank you for this document. I think this is an important
> document which
>     > should move forward, but I would like to discuss some points
> before it does
>     > so. These might result in simple clarifications, or might
> require more
>     > discussion, but I do hope they help improve the document.
>     >
>     > General comments:
>     >
>     > I found confusing to understand how optional or mandatory is the
> use of
>     > CBOR for profiles of this specification compared to the
> transport used. I
>     > understand the need for flexibility, but maybe it should be
> clarified the
>     > implication of using CoAP (is CBOR mandatory then?) vs HTTP (is
> CBOR always
>     > permitted? How is the encoding in that case? Is the same media type
>     > application/ace+cbor used in that case?). Note also that while
> requests
>     > include the content type to use, both in case HTTP or CoAP+CBOR
> are used,
>     > the response don't seem to include this information.
>     >
>     > I would like it to be clarified what requirements (or even just
>     > recommendations) are there to use CoAP vs HTTP for different
> legs of the
>     > exchange - not necessarily remove the flexibility but to clarify for
>     > implementers what can be done and what would be the reasoning to do
>     > that: for example if both endpoints support HTTP with the AS,
> most likely you
>     > can have HTTP between C and RS, so does it really make sense to
> run this
>     > instead of OAuth 2.0? Right now all is permitted, but does it
> all make sense? I
>     > feel like this type of considerations are missing. As a note - I
> am not sure
>     > what allowing a different encoding than CBOR for any leg of the
> exchange
>     > adds to the specification - it makes things more confusing, and
> if needed it
>     > could be specified in another document.
>     >
>     > While going through and thinking about encodings (assuming we
> keep the
>     > doc as is with regards to allowing more than just CBOR), I
> wondered if it
>     > would be better to define a new media type to use when the ACE
>     > framework is used with HTTP, to differentiate from OAuth 2.0,
> since some of
>     > the endpoints used are the same (/token and /introspect at the AS).
> I am
>     > interested to hear more from my co-AD as well if this would be
> an OK use of
>     > a new media type - I am thinking of the case where AS is
> supporting both
>     > OAuth 2.0 and the Ace framework - or if it is unnecessary, since the
>     > encodings are the same, and the parameters are registered in
> OAuth
> 2.0
>     > registry.
>     >
>     > More detailed comments below.
>     > Francesca
>     >
>     >
>     >
> ----------------------------------------------------------------------
>     > COMMENT:
>     >
> ----------------------------------------------------------------------
>     >
>     > Detailed comments:
>     >
>     > 1. -----
>     >
>     >    sufficiently compact.  CBOR is a binary encoding designed for
> small
>     >    code and message size, which may be used for encoding of self
>     >    contained tokens, and also for encoding payloads transferred in
>     >    protocol messages.
>     >
>     > FP: "may be used" make it seem as if CBOR is always optional
> (even when
>     > CoAP is used). See points 11. and 13. for examples of text that
> seem to imply
>     > that CBOR is mandatory in some cases.
>     >
>     > 2. -----
>     >
>     >       Refresh tokens are issued to the client by the authorization
>     >       server and are used to obtain a new access token when the
> current
>     >       access token becomes invalid or expires, or to obtain
> additional
>     >
>     > FP: token validity - it is not clear what it means for a token
> to become invalid
>     > (vs expiring). As this is the first time it is mentioned, it
> should be explained
>     > here or referenced.
>     >
>     > 3. -----
>     >
>     >          An asymmetric key pair is generated on the token's recipient
>     >          and the public key is sent to the AS (if it does not already
>     >
>     >           inside the token and sent back to the requesting party.
> The
>     >          consumer of the token can identify the public key from the
>     >
>     >  FP: "token's recipient" and "consumer of the token" - why not
> talk about
>     > client and resource server here? It would fit better with the
> terminology
>     > used  in the rest of the document.
>     >
>     >  4. -----
>     >
>     >     This framework RECOMMENDS the use of CoAP as replacement for HTTP
>     > for
>     >    use in constrained environments.  For communication security this
>     >
>     > FP: This was already stated in the introduction in the following
> sentence:
>     >
>     >    of processing capabilities, available memory, etc.  For web
>     >    applications on constrained nodes, this specification RECOMMENDS
> the
>     >    use of the Constrained Application Protocol (CoAP) [RFC7252] as
>     >    replacement for HTTP.
>     >
>     > Not sure repeating is useful.
>     >
>     > 5. -----
>     >
>     >    OAuth 2.0 (such as [RFC7521] and [RFC8628]).  What grant types
> works
>     >    best depends on the usage scenario and [RFC7744] describes many
>     >    different IoT use cases but there are two preferred grant types,
>     >    namely the Authorization Code Grant (described in Section 4.1 of
>     >
>     > FP: nit: s/works/work . I think "preferred" is probably not the
> right term
>     > here, and should be rephrased or clarified - preferred respect to?
>     >
>     > 6. -----
>     >
>     >       In addition to the response parameters defined by OAuth 2.0 and
>     >       the PoP access token extension, this framework defines
> parameters
>     >       that can be used to inform the client about capabilities of the
>     >       RS, e.g. the profiles the RS supports.  More information about
>     >
>     > FP: I believe this is a leftover from a previous version of the
> document, but
>     > should be "profile" and not "profiles" as the AS is only allowed to
>     > communicate one profile to the client and RS - see for example
> the following
>     > sentences:
>     >
>     >       The Client and the RS mutually authenticate using the security
>     >       protocol specified in the profile (see step B) and the keys
>     >
>     >       The AS informs the client of the selected profile using the
>     >       "ace_profile" parameter in the token response.
>     >
>     > 7. -----
>     >
>     >          (1) the client sends the access token containing, or
>     >          referencing, the authorization information to the RS, that
> may
>     >          be used for subsequent resource requests by the client, and
>     >
>     > FP: s/may/will
>     >
>     > 8. -----
>     >
>     >       While the structure and encoding of the access token varies
>     >       throughout deployments, a standardized format has been defined
>     >       with the JSON Web Token (JWT) [RFC7519] where claims are
> encoded
>     >       as a JSON object.  In [RFC8392], an equivalent format using
> CBOR
>     >       encoding (CWT) has been defined.
>     >
>     > FP: Would it make sense to RECOMMEND the use of JWT when HTTP is
> used?
>     > Or is CWT always RECOMMENDED?
>     >
>     > 9. -----
>     >
>     >    parameters.  When profiles of this framework use CoAP instead, it
> is
>     >    REQUIRED to use of the following alternative instead of Uri-query
>     >    parameters: The sender (client or RS) encodes the parameters of
> its
>     >    request as a CBOR map and submits that map as the payload of the
> POST
>     >    request.
>     >
>     > FP: I think it should be better defined (or at least hinted in
> this
> paragraph)
>     > the mapping between the CBOR encoded parameters and the Uri-query
>     > parameters:
>     > are they all encoded as CBOR text strings?
>     >
>     > 10. -----
>     >
>     >    Applications that use this media type: The type is used by
>     >    authorization servers, clients and resource servers that support
> the
>     >    ACE framework as specified in [this document].
>     >
>     > FP: I suggest adding "that support the ACE framework with CBOR
> encoding,
>     > as specified ..."
>     >
>     > 11. -----
>     >
>     >    The OAuth 2.0 AS uses a JSON structure in the payload of its
>     >    responses both to client and RS.  If CoAP is used, it is REQUIRED
> to
>     >    use CBOR [RFC8949] instead of JSON.  Depending on the profile, the
>     >    CBOR payload MAY be enclosed in a non-CBOR cryptographic wrapper
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