> > Yes, as I said before, authorization servers are free to enforce one-time > use of the authorization code even if there isn't a requirement to. The > proposal is just to remove the *requirement* of authorization servers > enforcing it. >
I agree, and therefore I think what it really ought to be is "MAY". Annabelle said: > There are legitimate use cases for a client to replay an authorization > code. Connection failures happen. Servers fall over before completing > requests. Users hit browser refresh buttons. Permitting replay of > authorization codes (assuming valid PKCE, client creds, etc.) allows > clients to handle these failure modes simply and gracefully via retries. Couldn't agree more. Having experienced these exact use-cases, I can honestly say that denying users a smooth experience just to be compliant with the spec, which offers no additional security if PKCE is also being used, makes no sense. It is also more effort (from a repository layer perspective) to implement one-time use than do PKCE verification. What is the practical reason for allowing "plain" PKCE in OAuth 2.1? Are > there really use cases out there where SHA-256 is a deal breaker? > I'd be interested in these use-cases as well (I can't think of any). On Thu, Oct 14, 2021 at 8:36 AM Aaron Parecki <aa...@parecki.com> wrote: > Yes, as I said before, authorization servers are free to enforce one-time > use of the authorization code even if there isn't a requirement to. The > proposal is just to remove the *requirement* of authorization servers > enforcing it. > > I am okay with Mike's suggestion of changing the language to "SHOULD" to > continue to point out the possibility of enforcing one-time authorization > codes if desired. > > > > On Wed, Oct 13, 2021 at 2:15 PM Pieter Kasselman < > pieter.kassel...@microsoft.com> wrote: > >> Log files can exist in lots of place (clients, servers, data lakes). The >> question is whether it is a valid assumption that an attacker cannot obtain >> an Authorization Code and a Code Verifier and present it a second time >> round. Limiting the validity period is one layer of defence, PKCE is >> another layer, one time use enforcement is another. Assuming breach and >> designing from a defence in depth perspective is a good practice, so why >> not give implementors options (and guidance) to add additional layers of >> defence to match their risk profiles? >> >> >> >> >> >> *From:* OAuth <oauth-boun...@ietf.org> *On Behalf Of *Sascha Preibisch >> *Sent:* Wednesday 13 October 2021 22:06 >> *To:* Aaron Parecki <aa...@parecki.com> >> *Cc:* IETF oauth WG <oauth@ietf.org> >> *Subject:* Re: [OAUTH-WG] [EXTERNAL] Re: Authorization code reuse and >> OAuth 2.1 >> >> >> >> Ok, if the goal is to avoid unnecessary requirements I am suggesting to >> point out why MUST was changed to SHOULD. Otherwise developers will start >> to mix and match OAuth 2.0 and OAuth 2.1 requirements as they see them fit >> their needs. >> >> In regards to encrypted values in PKCE, Aaron, I can also not confirm >> that as the general implementation. >> >> >> >> On Wed, 13 Oct 2021 at 13:56, Aaron Parecki <aa...@parecki.com> wrote: >> >> The PKCE spec actually says "Typically, the "code_challenge" and >> "code_challenge_method" values are stored in encrypted form in the "code" >> itself" which I feel like might be a stretch to say that's typical, but >> this scenario was clearly thought of ahead of time. Doing that would enable >> an AS to avoid storing server-side state. >> >> >> >> On Wed, Oct 13, 2021 at 1:50 PM Sascha Preibisch < >> saschapreibi...@gmail.com> wrote: >> >> 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 <aa...@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 <wpa...@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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fauthress.io%2F&data=04%7C01%7Cpieter.kasselman%40microsoft.com%7C93c20c9c80354c77c10708d98e8d6776%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637697560293904430%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=vwcfj%2FVB8a84yDoAmqkXraWyqjOfWGrV08XdtZLWMXw%3D&reserved=0> >> . >> >> >> >> >> >> On Wed, Oct 13, 2021 at 10:33 PM Aaron Parecki <aa...@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.kassel...@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-boun...@ietf.org> *On Behalf Of *Aaron Parecki >> *Sent:* Wednesday 13 October 2021 18:40 >> *To:* Warren Parad <wparad=40rhosys...@dmarc.ietf.org> >> *Cc:* Mike Jones <Michael.Jones=40microsoft....@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...@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%7C93c20c9c80354c77c10708d98e8d6776%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637697560293914390%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=9LtSUyb7WjZQqY%2FBnFy47HxchMNGZG6Qx82hj%2Bd9X04%3D&reserved=0> >> . >> >> >> >> >> >> On Wed, Oct 13, 2021 at 7:17 PM Mike Jones <Michael.Jones= >> 40microsoft....@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%7C93c20c9c80354c77c10708d98e8d6776%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637697560293914390%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=gWX04yAEt3IP7lWFDS0zBzyJN8nvNfEf6Eq7i6qU7fM%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%7C93c20c9c80354c77c10708d98e8d6776%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637697560293924344%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=yk%2FjfwfllrczSKVwzH4Bt7GTr9TV8fSda2oZhV0ejyA%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%7C93c20c9c80354c77c10708d98e8d6776%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637697560293924344%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=yk%2FjfwfllrczSKVwzH4Bt7GTr9TV8fSda2oZhV0ejyA%3D&reserved=0> >> >> _______________________________________________ > OAuth mailing list > OAuth@ietf.org > https://www.ietf.org/mailman/listinfo/oauth >
_______________________________________________ OAuth mailing list OAuth@ietf.org https://www.ietf.org/mailman/listinfo/oauth
