[Openid-specs-fapi] Duplicate kids in jwks

Brian Campbell bcampbell at pingidentity.com
Fri Jan 17 20:59:46 UTC 2020

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

On Fri, Jan 17, 2020 at 12:50 AM Joseph Heenan via Openid-specs-fapi <
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:
> https://bitbucket.org/openid/connect/issues/1127
> 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 - any opinions (positive
> & negative) would be great please.
> Thanks
> Joseph Heenan
> OpenID Certification Team
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