Re: [OAUTH-WG] [EXTERNAL] Re: Authorization code reuse and OAuth 2.1

If the challenge is based on distributed authorization server
configurations, how would they handle PKCE? I imagine that managing the
state for PKCE is not less challenging than managing authorization codes on
the server side, preventing reuse of them.
With that in mind I am not sure if I follow the given argument. I would
prefer to keep MUST as it is today.

On Wed, 13 Oct 2021 at 13:37, Aaron Parecki <aaron@parecki.com> wrote:

> HTTPS, because if that's broken then the rest of OAuth falls apart too.
>
> On Wed, Oct 13, 2021 at 1:36 PM Warren Parad <wparad@rhosys.ch> wrote:
>
>> I feel like I'm missing something, what stops just plain old network
>> sniffing and replying the whole encrypted payload to the AS and getting
>> back a valid token?
>>
>> Warren Parad
>>
>> Founder, CTO
>> Secure your user data with IAM authorization as a service. Implement
>> Authress <https://authress.io/>.
>>
>>
>> On Wed, Oct 13, 2021 at 10:33 PM Aaron Parecki <aaron@parecki.com> wrote:
>>
>>> Aside from the "plain" method, the PKCE code verifier never leaves the
>>> client until it's sent along with the authorization code in the POST
>>> request to the token endpoint. The only place it can leak at that point is
>>> if the authorization server itself leaks it. If you have things leaking
>>> from the authorization server log, you likely have much bigger problems
>>> than authorization code replays.
>>>
>>> Keep in mind that even with the proposed change to drop the requirement
>>> of authorization codes being one time use, authorization servers are free
>>> to enforce this still if they want. Authorization code lifetimes are still
>>> expected to be short lived as well.
>>>
>>> Aaron
>>>
>>>
>>> On Wed, Oct 13, 2021 at 1:25 PM Pieter Kasselman <
>>> pieter.kasselman@microsoft.com> wrote:
>>>
>>>> Aaron, I was curious what prevents an attacker from presenting an
>>>> Authorization Code and a PKCE Code Verifier for a second time if the one
>>>> time use requirement is removed. Is there another countermeasure in  PKCE
>>>> that would prevent it? For example, an attacker may obtain the
>>>> Authorization Code and the Code Verifier from a log and replay it.
>>>>
>>>>
>>>>
>>>> Cheers
>>>>
>>>>
>>>>
>>>> Pieter
>>>>
>>>>
>>>>
>>>> *From:* OAuth <oauth-bounces@ietf.org> *On Behalf Of *Aaron Parecki
>>>> *Sent:* Wednesday 13 October 2021 18:40
>>>> *To:* Warren Parad <wparad=40rhosys.ch@dmarc.ietf.org>
>>>> *Cc:* Mike Jones <Michael.Jones=40microsoft.com@dmarc.ietf.org>;
>>>> oauth@ietf.org
>>>> *Subject:* [EXTERNAL] Re: [OAUTH-WG] Authorization code reuse and
>>>> OAuth 2.1
>>>>
>>>>
>>>>
>>>> Warren, I didn't see you on the interim call, so you might be missing
>>>> some context.
>>>>
>>>>
>>>>
>>>> The issue that was discussed is that using PKCE already provides all
>>>> the security benefit that is gained by enforcing single-use authorization
>>>> codes. Therefore, requiring that they are single-use isn't necessary as it
>>>> doesn't provide any additional benefit.
>>>>
>>>>
>>>>
>>>> If anyone can think of a possible attack by allowing authorization
>>>> codes to be reused *even with a valid PKCE code verifier* then that would
>>>> warrant keeping this requirement.
>>>>
>>>>
>>>>
>>>> ---
>>>>
>>>> Aaron Parecki
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Wed, Oct 13, 2021 at 10:27 AM Warren Parad <wparad=
>>>> 40rhosys.ch@dmarc.ietf.org> wrote:
>>>>
>>>> Isn't it better for it to be worded as we want it to be, with the
>>>> implication being that of course it might be difficult to do that, but that
>>>> AS devs will think long and hard about sometimes not denying the request?
>>>> Even with MUST, some AS will still allow reuse of auth codes. Isn't that
>>>> better than flat out saying: *sure, there's a valid reason*
>>>>
>>>>
>>>>
>>>> In other words, how do we think about RFCs? Do they exist to be
>>>> followed to the letter or not at all? Or do they exist to stipulate this is
>>>> the way, but acknowledge that not everyone will build a solution that holds
>>>> them as law.
>>>>
>>>>
>>>>
>>>> Let's look at *SHOULD*
>>>>
>>>> This word, or the adjective "RECOMMENDED", mean that there may exist
>>>> valid reasons in particular circumstances to ignore a particular item, but
>>>> the full implications must be understood and carefully weighed before
>>>> choosing a different course.
>>>>
>>>>
>>>>
>>>> I think *recommended* here is not sufficient nor are there valid
>>>> reasons. "It's too hard" isn't really a valid reason. Isn't it better in
>>>> this case for an AS to not be compliant with the RFC, than it is to relax
>>>> this to SHOULD and have lots of AS thinking reusing auth codes is a viable
>>>> solution, "because they are a special snowflake where SHOULD should apply".
>>>>
>>>>
>>>>
>>>> Are we setting the standard or instead attempting to sustain a number
>>>> of "AS that are in compliance with the RFC"?
>>>>
>>>>
>>>>
>>>> *Warren Parad*
>>>>
>>>> Founder, CTO
>>>>
>>>> Secure your user data with IAM authorization as a service. Implement
>>>> Authress
>>>> <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fauthress.io%2F&data=04%7C01%7Cpieter.kasselman%40microsoft.com%7C64289cdc8a4743659b3108d98e70a5d1%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637697436788333255%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=lw%2BH1z1Ut9kr6S%2F4aVsPmcErAcZx0eK2WV78OlEl2dU%3D&reserved=0>
>>>> .
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Wed, Oct 13, 2021 at 7:17 PM Mike Jones <Michael.Jones=
>>>> 40microsoft.com@dmarc.ietf.org> wrote:
>>>>
>>>> During today’s call, it was asked whether we should drop the OAuth 2.0
>>>> language that:
>>>>
>>>>          The client MUST NOT use the authorization code
>>>>
>>>>          more than once.  If an authorization code is used more than
>>>>
>>>>          once, the authorization server MUST deny the request and SHOULD
>>>>
>>>>          revoke (when possible) all tokens previously issued based on
>>>>
>>>>          that authorization code.”
>>>>
>>>>
>>>>
>>>> The rationale given was that enforcing one-time use is impractical in
>>>> distributed authorization server deployments.
>>>>
>>>>
>>>>
>>>> Thinking about this some more, at most, we should relax this to:
>>>>
>>>>          The client MUST NOT use the authorization code
>>>>
>>>>          more than once.  If an authorization code is used more than
>>>>
>>>>          once, the authorization server SHOULD deny the request and
>>>> SHOULD
>>>>
>>>>          revoke (when possible) all tokens previously issued based on
>>>>
>>>>          that authorization code.”
>>>>
>>>>
>>>>
>>>> In short, it should remain illegal for the client to try to reuse the
>>>> authorization code.  We can relax the MUST to SHOULD in the server
>>>> requirements in recognition of the difficulty of enforcing the MUST.
>>>>
>>>>
>>>>
>>>> Code reuse is part of some attack scenarios.  We must not sanction it.
>>>>
>>>>
>>>>
>>>>                                                           -- Mike
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> OAuth mailing list
>>>> OAuth@ietf.org
>>>> https://www.ietf.org/mailman/listinfo/oauth
>>>> <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Fmailman%2Flistinfo%2Foauth&data=04%7C01%7Cpieter.kasselman%40microsoft.com%7C64289cdc8a4743659b3108d98e70a5d1%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637697436788343208%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ySJjihVbfLJJ85RtjNzEIMSPwe7kLZB8RKT8Ky3fYiA%3D&reserved=0>
>>>>
>>>> _______________________________________________
>>>> OAuth mailing list
>>>> OAuth@ietf.org
>>>> https://www.ietf.org/mailman/listinfo/oauth
>>>> <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Fmailman%2Flistinfo%2Foauth&data=04%7C01%7Cpieter.kasselman%40microsoft.com%7C64289cdc8a4743659b3108d98e70a5d1%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637697436788343208%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ySJjihVbfLJJ85RtjNzEIMSPwe7kLZB8RKT8Ky3fYiA%3D&reserved=0>
>>>>
>>>> _______________________________________________
> OAuth mailing list
> OAuth@ietf.org
> https://www.ietf.org/mailman/listinfo/oauth
>