Re: [OAUTH-WG] OAuth 2.1 - require PKCE?

Aaron Parecki <aaron@parecki.com> Wed, 06 May 2020 19:28 UTC

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From: Aaron Parecki <aaron@parecki.com>
Date: Wed, 6 May 2020 12:28:39 -0700
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To: Steinar Noem <steinar@udelt.no>
Cc: Phillip Hunt <phil.hunt@independentid.com>, Mike Jones <Michael.Jones=40microsoft.com@dmarc.ietf.org>, "oauth@ietf.org" <oauth@ietf.org>
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Subject: Re: [OAUTH-WG] OAuth 2.1 - require PKCE?
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I should add that even some OpenID Connect profiles require PKCE, such as
FAPI:

https://openid.net/specs/openid-financial-api-part-1.html#authorization-server

So the precedent for requiring PKCE already exists within some OpenID
Connect profiles.

On Wed, May 6, 2020 at 12:23 PM Aaron Parecki <aaron@parecki.com> wrote:

> Yes, and also, many of those providers very likely already support PKCE
> already. Skimming through that list of certified OPs, I recognize many
> names there from providers that I know support PKCE.
>
> On Wed, May 6, 2020 at 12:18 PM Steinar Noem <steinar@udelt.no> wrote:
>
>> So, wouldn't a MUST just mean that we would have some OPs that are 2.1
>> compliant and some that aren't?
>>
>> ons. 6. mai 2020 kl. 21:12 skrev Phillip Hunt <
>> phil.hunt@independentid.com>gt;:
>>
>>> Mike,
>>>
>>> The point of 2.1 is to raise the security bar.
>>>
>>> Yes it adds new MUST requirements.
>>>
>>> But what about OIDC would break other than required implementation of
>>> PKCE to support 2.1?
>>>
>>> Eg Would additional signaling be required to facilitate interoperability
>>> and migration between versions? Would that be an oauth issue or an OIDC one?
>>>
>>> Phil
>>>
>>> On May 6, 2020, at 11:56 AM, Aaron Parecki <aaron@parecki.com> wrote:
>>>
>>> 
>>> > In particular, authorization servers shouldn’t be required to support
>>> PKCE when they already support the OpenID Connect nonce.
>>>
>>> The Security BCP already requires that ASs support PKCE:
>>> https://tools.ietf.org/html/draft-ietf-oauth-security-topics-15#section-2.1.1 Are
>>> you suggesting that the Security BCP change that requirement as well? If
>>> so, that's a discussion that needs to be had ASAP. If not, then that's an
>>> implicit statement that it's okay for OpenID Connect implementations to not
>>> be best-practice OAuth implementations. And if that's the case, then I also
>>> think it's acceptable that they are not complete OAuth 2.1 implementations
>>> either.
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Wed, May 6, 2020 at 11:21 AM Mike Jones <Michael.Jones=
>>> 40microsoft.com@dmarc.ietf.org> wrote:
>>>
>>>> The disadvantage of requiring PKCE for OpenID Connect implementations
>>>> is that you’re trying to add a normative requirement that’s not required of
>>>> OpenID Connect deployments today, which would bifurcate the ecosystem.
>>>> There are hundreds of implementations (including the 141 certified ones at
>>>> https://openid.net/certification/), none of which have ever been
>>>> required to support PKCE.  Therefore, most don’t.
>>>>
>>>>
>>>>
>>>> Per feedback already provided, I believe that OAuth 2.1 should align
>>>> with the guidance already in the draft Security BCP, requiring EITHER the
>>>> use of PKCE or the OpenID Connect nonce.  Trying to retroactively impose
>>>> unnecessary requirements on existing deployments is unlikely to succeed and
>>>> will significantly reduce the relevance of the OAuth 2.1 effort.
>>>>
>>>>
>>>>
>>>> In particular, authorization servers shouldn’t be required to support
>>>> PKCE when they already support the OpenID Connect nonce.  And clients
>>>> shouldn’t reject responses from servers that don’t support PKCE when they
>>>> do contain the OpenID Connect nonce.  Doing so would unnecessarily break
>>>> things and create confusion in the marketplace.
>>>>
>>>>
>>>>
>>>>                                                           -- Mike
>>>>
>>>>
>>>>
>>>> *From:* OAuth <oauth-bounces@ietf.org> *On Behalf Of * Dick Hardt
>>>> *Sent:* Wednesday, May 6, 2020 10:48 AM
>>>> *To:* oauth@ietf.org
>>>> *Subject:* [OAUTH-WG] OAuth 2.1 - require PKCE?
>>>>
>>>>
>>>>
>>>> Hello!
>>>>
>>>>
>>>>
>>>> We would like to have PKCE be a MUST in OAuth 2.1 code flows. This is
>>>> best practice for OAuth 2.0. It is not common in OpenID Connect servers as
>>>> the nonce solves some of the issues that PKCE protects against. We think
>>>> that most OpenID Connect implementations also support OAuth 2.0, and
>>>> hence have support for PKCE if following best practices.
>>>>
>>>>
>>>>
>>>> The advantages or requiring PKCE are:
>>>>
>>>>
>>>>
>>>> - a simpler programming model across all OAuth applications and
>>>> profiles as they all use PKCE
>>>>
>>>>
>>>>
>>>> - reduced attack surface when using  S256 as a fingerprint of the
>>>> verifier is sent through the browser instead of the clear text value
>>>>
>>>>
>>>>
>>>> - enforcement by AS not client - makes it easier to handle for client
>>>> developers and AS can ensure the check is conducted
>>>>
>>>>
>>>>
>>>> What are disadvantages besides the potential impact to OpenID Connect
>>>> deployments? How significant is that impact?
>>>>
>>>>
>>>>
>>>> Dick, Aaron, and Torsten
>>>>
>>>>
>>>>
>>>> ᐧ
>>>> _______________________________________________
>>>> OAuth mailing list
>>>> OAuth@ietf.org
>>>> https://www.ietf.org/mailman/listinfo/oauth
>>>>
>>> _______________________________________________
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>>>
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>>>
>>
>>
>> --
>> Vennlig hilsen
>>
>> Steinar Noem
>> Partner Udelt AS
>> Systemutvikler
>>
>> | steinar@udelt.no | hei@udelt.no  | +47 955 21 620 | www.udelt.no |
>>
>