Hi Tobias,

On Wed, Dec 14, 2022 at 2:49 AM Tobias Looker <tobias.looker=
40mattr.glo...@dmarc.ietf.org> wrote:

>
> There are certainly things we could explore here, one such option could be
> to continue to only return application/json but for the document to include
> an element like "@context" in the response if its desired that the metadata
> be processable as a JSON-LD document.
>

I'd generally agree; my only concern about the Content-type is that it
could be set by the web server rather than the developer, and developers
might have no control over the web server configuration. If, for example,
the metadata is deployed as a static JSON-LD file, and the web server uses
MIME DB, then it will serve the resource as application/ld+json rather than
application/json (unless reconfigured to do so).


>
> Yes I've had similar thoughts about this, I think RFC 9111 could be a good
> basis. What remains a little unclear to me is what normative requirements
> we might impose on implementers in regards to caching, for instance I think
> requiring clients hosting their metadata to implement HTT request caching
> would be too strict, but if they are to implement it, RFC 9111 is
> recommended and if you do here is how it must be implemented?
>

I agree that requiring clients to implement caching (i.e. to guarantee Age
and Cache-Control headers) might be excessively strict. But in the case
where the headers are not present, I think we should recommend the ASes to
implement some opinionated defaults (e.g., default TTL for client metadata
= 1 hour etc.)

Dmitry


>
> Thanks,
>
> [image: Mattr website]
> <https://aus01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fscanmail.trustwave.com%2F%3Fc%3D15517%26d%3Dw46s4eMXULV_ns1ZfAKYLbVKcqey_PHiW1WeN4boYw%26u%3Dhttps%253a%252f%252fmattr.global%252f&data=04%7C01%7CSteve.Lowes%40mbie.govt.nz%7C5a65fe33c70b41fd8ba908d976f3a2f1%7C78b2bd11e42b47eab0112e04c3af5ec1%7C0%7C0%7C637671611076709977%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=tKqCMzLUQNCeORd908YqfqZoT7tCy%2FMVwXdjpch1sDY%3D&reserved=0>
>
>
>
> *Tobias Looker*
>
> MATTR
> CTO
>
> +64 (0) 27 378 0461
> tobias.looker@mattr.global
>
> [image: Mattr website]
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> [image: Mattr on LinkedIn]
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>
>
> This communication, including any attachments, is confidential. If you are
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>
> ------------------------------
> *From:* Dmitry Telegin <dmitryt=40backbase....@dmarc.ietf.org>
> *Sent:* 14 December 2022 06:30
> *To:* Tobias Looker <tobias.looker@mattr.global>
> *Cc:* Ben Schwartz <bem...@google.com>; oauth@ietf.org <oauth@ietf.org>
> *Subject:* Re: [OAUTH-WG] OAuth2 Client Discovery
>
> EXTERNAL EMAIL: This email originated outside of our organisation. Do not
> click links or open attachments unless you recognise the sender and know
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>
> Hello Tobias, thanks for the draft! In regards to prior art, I'd like to
> mention Solid Project and their OIDC flavor, Solid-OIDC:
> https://solid.github.io/solid-oidc/#clientids-document
>
> They're using a similar approach (and have been for years), though with
> some differences:
> - client_id points to a URL that must resolve to the client metadata
> document directly (no .well-known/* used);
> - the document's format is JSON-LD, a superset of JSON.
>
> In order to maintain compatibility with Solid and similar existing
> technologies, would it make sense to mention that:
> - while retrieving client metadata, AS should recognize not only
> application/json, but application/ld+json (or maybe even
> application/*+json, as per
> https://datatracker.ietf.org/doc/html/rfc6839#section-3-1)?
> - any unknown fields (like JSON-LD "@context") must be ignored?
>
> On an unrelated note, it would be nice to cover the issue of caching the
> client metadata on the AS side. Obviously, we wouldn't want to re-request
> the metadata upon every request to the authorization endpoint. Would RFC
> 9111 suffice here? If so, which subset should be guaranteed to be supported
> by the AS?
>
> Thanks,
> Dmitry
>
> On Wed, Nov 9, 2022 at 8:36 PM Tobias Looker <tobias.looker=
> 40mattr.glo...@dmarc.ietf.org> wrote:
>
> Hi Ben,
>
> See below for some thoughts.
>
> > I'm having trouble understanding the precise URL structures that are
> used here.  Can client_uri include a nontrivial path?  Why is it necessary
> to repeat client_uri in the response JSON?
>
> The intent here is to follow how "OAuth 2.0 authorization metadata" works
> (RFC 8414) which requires the client resolving the authorization server
> metadata to check that the issuer in the resolved document matches the
> issuer URL they started the resolution with, see below for the relevant
> extract from RFC 8414.
>
> "
>
> The "issuer" value returned MUST be identical to the authorization
>    server's issuer identifier value into which the well-known URI string
>    was inserted to create the URL used to retrieve the metadata.  If
>    these values are not identical, the data contained in the response
>    MUST NOT be used.
>
>
> "
>
> So the equivalent with our draft is to require the authorization server to
> validate that the client_uri returned in the clients metadata response
> matches the URL that was used to retrieve the metadata.
>
> > The use of .well-known is a bit unusual.  Why not just host the JSON at
> the client_uri?
>
> Just to clarify it is, just under a well-known path? e.g if the client uri
> is https://client.example.com then the metadata would be published at
> https://client.example.com/.well-known/oauth-client
>
> > Finally, I note that the section on Impersonation Attacks doesn't
> mention the client_name or logo_uri.  If these are to be shown to the user,
> they present a very serious impersonation risk that ought to be discussed.
> (The client_name also might need to be localized, which could be done by
> fetching the JSON document with an appropriate Accept-Language request
> header.)
>
> Yes absolutely agree this is an important security consideration to
> highlight, I will capture an issue.
>
>
> Thanks,
>
> [image: Mattr website]
> <https://aus01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fscanmail.trustwave.com%2F%3Fc%3D15517%26d%3Dw46s4eMXULV_ns1ZfAKYLbVKcqey_PHiW1WeN4boYw%26u%3Dhttps%253a%252f%252fmattr.global%252f&data=04%7C01%7CSteve.Lowes%40mbie.govt.nz%7C5a65fe33c70b41fd8ba908d976f3a2f1%7C78b2bd11e42b47eab0112e04c3af5ec1%7C0%7C0%7C637671611076709977%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=tKqCMzLUQNCeORd908YqfqZoT7tCy%2FMVwXdjpch1sDY%3D&reserved=0>
>
>
>
> *Tobias Looker*
>
> MATTR
> CTO
>
> +64 (0) 27 378 0461
> tobias.looker@mattr.global
>
> [image: Mattr website]
> <https://aus01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fscanmail.trustwave.com%2F%3Fc%3D15517%26d%3Dw46s4eMXULV_ns1ZfAKYLbVKcqey_PHiW1WeN4boYw%26u%3Dhttps%253a%252f%252fmattr.global%252f&data=04%7C01%7CSteve.Lowes%40mbie.govt.nz%7C5a65fe33c70b41fd8ba908d976f3a2f1%7C78b2bd11e42b47eab0112e04c3af5ec1%7C0%7C0%7C637671611076709977%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=tKqCMzLUQNCeORd908YqfqZoT7tCy%2FMVwXdjpch1sDY%3D&reserved=0>
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>
>
> This communication, including any attachments, is confidential. If you are
> not the intended recipient, you should not read it - please contact me
> immediately, destroy it, and do not copy or use any part of this
> communication or disclose anything about it. Thank you. Please note that
> this communication does not designate an information system for the
> purposes of the Electronic Transactions Act 2002.
>
> ------------------------------
> *From:* Ben Schwartz <bemasc=40google....@dmarc.ietf.org>
> *Sent:* 10 November 2022 07:04
> *To:* Tobias Looker <tobias.looker@mattr.global>
> *Cc:* oauth@ietf.org <oauth@ietf.org>
> *Subject:* Re: [OAUTH-WG] OAuth2 Client Discovery
>
> EXTERNAL EMAIL: This email originated outside of our organisation. Do not
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