[Openid-specs-fapi] [EXTERNAL] Re: Duplicate kids in jwks

Mike Jones Michael.Jones at microsoft.com
Fri Jan 17 22:02:00 UTC 2020

Filip is correct.  The intent is only to enforce this behavior in certified implementations – not to change the specifications.  This is being done to increase interoperability.

There’s lots of cases where we intentionally constrain certified implementations beyond what’s strictly required by the specifications to increase interoperability.  For instance, the test “(OP-IDToken-kid) IDToken has kid [Basic, Implicit, Hybrid]” requires that the ID Token always contains a Key ID, even though the Connect spec only requires it when there are multiple keys in the JWK Set.  This was done so that it could be counted on.

Likewise, the WG decision to require unique “kid” values goes beyond the spec, but eliminates a number of potential errors resulting from odd corner cases.  I firmly believe that the working made the right call to enforce this in the certification suite.

                                                          -- Mike

From: Openid-specs-fapi <openid-specs-fapi-bounces at lists.openid.net> On Behalf Of Filip Skokan via Openid-specs-fapi
Sent: Friday, January 17, 2020 1:42 PM
To: Financial API Working Group List <openid-specs-fapi at lists.openid.net>
Cc: Filip Skokan <panva.ip at gmail.com>
Subject: [EXTERNAL] Re: [Openid-specs-fapi] Duplicate kids in jwks

I don’t think it’s clear whether the intent was an errata or a proposal to the WG to further constrain the Connect certification profile.

I believe we could only do the latter.
Odesláno z iPhonu

17. 1. 2020 v 22:05, Brian Campbell via Openid-specs-fapi <openid-specs-fapi at lists.openid.net<mailto:openid-specs-fapi at lists.openid.net>>:

For better or worse JOSE allowed for duplicate kids and Connect didn't constrain it. So requiring uniqueness is a breaking change that an erratum shouldn't be doing. I guess that counts as a negative opinion towards the decision in https://bitbucket.org/openid/connect/issues/1127<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbitbucket.org%2Fopenid%2Fconnect%2Fissues%2F1127&data=02%7C01%7CMichael.Jones%40microsoft.com%7C3551ece54c0549a9fb0008d79b962a4e%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637148942095112814&sdata=lqMLz%2BB19FKwQyV4z4m8hWZZ%2FrAJArE6Pd84xfRaBdk%3D&reserved=0>

On Fri, Jan 17, 2020 at 12:50 AM Joseph Heenan via Openid-specs-fapi <openid-specs-fapi at lists.openid.net<mailto:openid-specs-fapi at lists.openid.net>> wrote:
Hi all,

I wanted to direct the FAPI working group to this discussion within the Connect working group:


Namely that duplicate kids are not permitted in JWKS.

A test for this was recently added to all the conformance tests, which caused one of the UK banks to opine:

it is valid for the JWK endpoint to return multiple KID instances, one for each ‘alg’ supported?
The spec calls for the alg PS256 or longer to be supported, so we also have (for instance) PS384, PS512. And although we may show a couple that we don’t need, my point is that it must be valid to show multiple key entries to support multiple valid alg values.

To some extent this seems a reasonable point, reusing a key across across two algs that can use the same key seems ok, and arguably perhaps better than having the key once without an ‘alg’ specified.

As this affects the FAPI certification tests, I wanted to check the FAPI WG agrees with the decision in https://bitbucket.org/openid/connect/issues/1127<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbitbucket.org%2Fopenid%2Fconnect%2Fissues%2F1127&data=02%7C01%7CMichael.Jones%40microsoft.com%7C3551ece54c0549a9fb0008d79b962a4e%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637148942095132801&sdata=V8UtOzKQhIeFFBnhGyaRUWQn1nLqGhTrIAm7vQakV1o%3D&reserved=0> - any opinions (positive & negative) would be great please.


Joseph Heenan
OpenID Certification Team

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