Re: [OAUTH-WG] WGLC Review of PAR

[Brian Campbell <[e-mail]>]

I'm not sure how to word it exactly but I think Dick has landed on what we
ultimately want this to say. Basically that the "request_uri" is intended
to be used only once, the client MUST not use it more than once, and that
the AS should also treat it as one-time use but may make reasonable
accommodations to more gracefully handle redundant authorization requests
due to browser reload or similar.

On Sun, Aug 30, 2020 at 4:48 PM Dick Hardt <[e-mail]> wrote:

> I don't have the context of the text to respond to the exact wording, but
> I think we can state that the client MUST use the "request_uri" only once,
> and then explain that the AS may receive duplicate requests if the browser
> is reloaded.
>
>
> On Sat, Aug 29, 2020 at 4:24 AM Torsten Lodderstedt <
> [e-mail]> wrote:
>
>> You are making a good point here. The reason we added the one time use
>> constraint was the fact the client will include parameters supposed to be
>> used only once, e.g. the PKCE code_challenge. For a traditional
>> authorisation request, we would recommend the client to use a per
>> transaction (== one time use) code_challenge, but PKCE does not require the
>> AS to enforce it. Mapping this to PAR means, we SHOULD recommend the client
>> to use the request_uri only once but not require the AS to enforce it.
>>
>> Would the following text work for you?
>>
>> Since parts of the request content, e.g. the "code_challenge"
>>    parameter value, is unique to a certain authorization request,
>> the client SHOULD use the "request_uri" only once.
>>
>> I also would move this text to section 4.
>>
>> > On 27. Aug 2020, at 18:11, Dick Hardt <[e-mail]> wrote:
>> >
>> > That is not correct.
>> >
>> > The authorization code one-time-use is directly between the client and
>> the AS. The client has a number of mechanisms to ensure it only presents
>> the authorization code to the AS once, such as a session that was set when
>> the user started at the client.
>> >
>> > In contrast, in a redirect from the client to the AS, the client loses
>> control on how many times the user-agent loads the URL at the AS.
>> Additionally, there is unlikely to be an active browser session at the AS,
>> so the AS can not easily differentiate between a URL load from the same
>> user, or different users. If one-time-use, one of them MUST fail. If the
>> two requests happen to be from the same user (because of a reload, which
>> the user did because the AS was slow to respond), there is no way for the
>> AS to know which of the requests is the one that is current in front of the
>> user. While the AS can internally ensure processing of the request once,
>> one-time-use would dictate that it provides a failure message to one of the
>> requests.
>> >
>> > /Dick
>> >
>> >
>> > ᐧ
>> >
>> > On Thu, Aug 27, 2020 at 7:17 AM Justin Richer <[e-mail]> wrote:
>> > We already have this same property with authorization codes, and it’s
>> managed today reasonably well (in my opinion). If you submit the same
>> request URI twice in the same browser (the refresh you’re talking about),
>> it shouldn’t start two separate authorization requests, but it would be
>> reasonable to detect that the same session attached to the same request URI
>> value showed up twice and continue the session as appropriate.
>> >
>> > None of this is in conflict with “one time use”, in my view, since
>> you’re actively detecting the session and source of the value.
>> >
>> >  — Justin
>> >
>> >> On Aug 26, 2020, at 6:16 PM, Dick Hardt <[e-mail]> wrote:
>> >>
>> >> I think one-time use may be overly restrictive, and I don't think it
>> is the property that we actually want.
>> >>
>> >> Give the request URI is in a redirect from the browser, there is a
>> good chance of a race condition where the same browser request is made more
>> than once, for example, while the browser is loading the authorization URL
>> at the AS, the user could refresh the page causing the authorization URL to
>> be reloaded. Would the reload count as a second use? One could argue it
>> either way.
>> >>
>> >> What I think we want from what I understand, is the request URI MUST
>> be unique so that there is no confusion on which request is being
>> referenced.
>> >>
>> >> I did not see anything about the expiry time of the request URI (but I
>> did not look super hard). If that is not there, then I think the request
>> URI MUST expire in a "short" period of time.
>> >>
>> >>
>> >>
>> >> ᐧ
>> >>
>> >> On Wed, Aug 26, 2020 at 1:45 PM Brian Campbell <bcampbell=
>> [e-mail]> wrote:
>> >> Thanks Justin. Just a couple more responses to responses inline below
>> (but with lots of content that needs no further discussion removed).
>> >>
>> >> A TL;DR for the WG is that I'd like to get some wider feedback on the
>> question of changing the one-time-use condition on the request_uri from a
>> SHOULD to a MUST.
>> >>
>> >> On Tue, Aug 25, 2020 at 4:57 PM Justin Richer <[e-mail]> wrote:
>> >> Hi Brian, just a couple responses inline where it seemed fitting.
>> Thanks for going through everything!
>> >>  — Justin
>> >>
>> >>> On Aug 25, 2020, at 6:01 PM, Brian Campbell <
>> [e-mail]> wrote:
>> >>>
>> >>> Thanks for the review and comments Justin. Replies (or attempts
>> thereat) are inline below.
>> >>>
>> >>>
>> >>> On Wed, Aug 19, 2020 at 2:06 PM Justin Richer <[e-mail]>
>> wrote:
>> >>> I’ve done a full read through of the PAR specification, and here are
>> my notes on it.
>> >>>
>> >>>
>> >>>     ¶2: Of necessity, this spec mixes parameters in the authorization
>> endpoint and token endpoint registries into a single request. Is there any
>> danger of conflict between them? The registry holds them in one list but
>> they could possibly have different semantics in both places..
>> >>>
>> >>> I think that technically such danger does exist but that it's highly
>> unlikely in practice. Especially because the only token endpoint parameters
>> that are relevant to PAR are those that deal with client authentication
>> (currently client_secret, client_assertion, and client_assertion_type). I'm
>> also not sure what can reasonably be done about it given the way the
>> registries are. I guess PAR could update the registration for those three
>> (client_secret, client_assertion, and client_assertion_type) to also
>> indicate authorization request as a usage location with some commentary
>> that it's only for avoiding name collisions. And offer some guidance about
>> doing the same for any future client auth methods being defined. But
>> honestly I'm not sure what, if anything, to do here?
>> >>>
>> >>> And yes it is super unfortunate that client auth and protocol
>> parameters got mixed together in the HTTP body. I didn't cause that
>> situation but I've certainly contributed to it and for that I apologize.
>> >>
>> >> I think the only perfect solution is to go back in time and fix the
>> registries with based on the last decade of knowledge in using them. :P
>> >>
>> >> For this, I think maybe being very prescriptive about the fact that
>> the only parameters from the token endpoint that are allowed here are those
>> used for client authentication and that when they show up, they’re
>> interpreted as in the token endpoint request not the authorization endpoint
>> request. Does that work?
>> >>
>> >> I think so, yes.. And will work on incorporating some text towards
>> that end.
>> >>
>> >>
>> >>
>> >>>     I don’t see why a request URI with unguessable values isn’t a
>> MUST for one-time-use, is there a reason?
>> >>>
>> >>> The reason AFAIK was to not be overly prescriptive and allow for
>> eventually consistent or not atomic storage of the data by not strictly
>> requiring the AS to enforce one-time-use. Do you think that's too loose or
>> could be worded/explained differently or better?
>> >>
>> >> I do think it’s too loose and it should be a MUST, and the methods for
>> enforcing that “MUST” are going to vary based on the deployments and
>> implementations out there.
>> >>
>> >>
>> >> I'd be okay with making it a MUST but think maybe it'd be good to hear
>> from a few more people in the WG before committing to that change.
>> >>
>> >> Can I ask some folks to weigh in on this one? I'm leaning towards
>> making the change barring objections.
>> >>
>> >>
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>> ᐧ
>

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