Re: [OAUTH-WG] WGLC Review of PAR
Dave Tonge <dave.tonge@momentumft.co.uk> Thu, 03 September 2020 12:14 UTC
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References: <7C0FD285-F677-4501-B2FB-9431A59855F6@mit.edu> <CA+k3eCRsBTvdhyzBOETxWLd6PJ61B2W4yY5QHv196amDFq7gnQ@mail.gmail.com> <B86967B1-3FA1-4ADA-BF9B-D34C693617C7@lodderstedt.net> <03845E0A-3563-4FF5-A3F9-318A1C928B89@mit.edu> <61CD8CC7-D16F-4D2A-A43E-2C80DC5B565A@lodderstedt.net> <CAHdPCmMxxXx-sc2wRSV4JXG4m6zqGwK+J_UgWdBh7jipqXA5fQ@mail.gmail.com> <57BB7167-377D-451C-891F-E04B9A10372F@mit.edu> <CA+k3eCQCKmM-pOLM6P6utOqiQF6jK4ZyQNx_gEFTZk6kDmczbA@mail.gmail.com>
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From: Dave Tonge <dave.tonge@momentumft.co.uk>
Date: Thu, 03 Sep 2020 14:14:25 +0200
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To: Brian Campbell <bcampbell=40pingidentity.com@dmarc.ietf.org>
Cc: Justin Richer <jricher@mit.edu>, oauth <oauth@ietf.org>
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Subject: Re: [OAUTH-WG] WGLC Review of PAR
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Looks really good to me, thanks Brian. On Wed, 2 Sep 2020 at 21:42, Brian Campbell <bcampbell= 40pingidentity.com@dmarc.ietf.org> wrote: > Thanks Torsten, Taka, and Justin, > > I took the revised text from Justin and tweaked it with some typo cleanup > and minor adjustments to make what is hopefully a final proposal below. I > had a similar feeling about the last paragraph not really fitting but don't > have a better location to suggest so am just leaving it. > > 2.4. Management of Client Redirect URIs > > While OAuth 2.0 [RFC6749] allows clients to use unregistered redirect_uri > values in certain circumstances, or for the authorization server to apply > its own matching semantics to the redirect_uri value presented by the > client at the authorization endpoint, the OAuth Security BCP > [I-D.ietf-oauth-security-topics] as well as OAuth 2.1 [I-D.ietf-oauth-v2-1] > require an authorization server exactly match the redirect_uri parameter > against the set of redirect URIs previously established for a particular > client. This is a means for early detection of client impersonation > attempts and prevents token leakage and open redirection. As a downside, > this can make client management more cumbersome since the redirect URI is > typically the most volatile part of a client policy. > > The exact matching requirement MAY be relaxed by the authorization server > for a confidential client using pushed authorization requests since the > authorization server authenticates the client before the authorization > process starts and thus ensures it is interacting with the legitimate > client. The authorization server MAY allow such clients to specify > redirect_uri values that were not previously registered with the > authorization server. This will give the client more flexibility (e.g. to > mint distinct redirect URI values per authorization server at runtime) and > can simplify client management. It is at the discretion of the > authorization server to apply restrictions on supplied redirect_uri values, > e.g. the authorization server MAY require a certain URI prefix or allow > only a query parameter to vary at runtime. > > The ability to set up transaction specific redirect URIs is also useful in > situations where client ids and corresponding credentials and policies are > managed by a trusted 3rd party, e.g. via client certificates containing > client permissions. Such an externally managed client could interact with > an authorization server trusting the respective 3rd party without the need > for an additional registration step. > > On Wed, Sep 2, 2020 at 8:09 AM Justin Richer <jricher@mit.edu> wrote: > >> The real conflict here is with the BCP and 2.1, both of which adopt the >> stricter matching semantics for redirect URIs than 6749 does on its own. >> This section would be needed to clarify how they relate to each other. That >> said, I think adding some of Taka’s observations to Torsten’s text wouldn’t >> hurt: >> >> 2.4. Management of redirect_uri >> >> While OAuth 2.0 [RFC6749] allows clients to use unregistered redirect_uri >> values in certain circumstances, or for the AS to apply its own matching >> semantics to the redirect_uri value presented by the client at the >> authorization endpoint, the OAuth Security BCP >> [I-D.ietf-oauth-security-topics] as well as OAuth 2.1 [I-D.ietf-oauth-v2-1] >> require an AS to excactly match the redirect_uri parameter against the set >> of redirect URIs previously established for a particular client. This is a >> means to early detect attempts to impersonate a client and prevent token >> leakage and open redirection. As a downside, it makes client management >> more complex since the redirect URI is typically the most volatile part of >> a client policy. >> >> This requirement MAY be relaxed by the AS if a confidential client uses >> pushed authorization requests since the AS authenticates the client before >> the authorization process starts and that way ensures it interacts with the >> legit client. The AS MAY allow such clients to specify redirect_uri values >> not previously registered with the AS. This will give the client more >> flexibility (e.g. to mint AS-specific redirect URIs on the fly) and makes >> client management much easier. It is at the discretion of the AS to apply >> restriction on redirect_uri values, e.g. the AS MAY require a certain URI >> prefix or allow only a query parameter to vary at runtime. >> >> I also feel like this paragraph belongs in a different section outside of >> here. I’m not sure where, but it doesn’t quite seem to fit, to me. It’s not >> the end of the world if it stays here though as it’s a decent view on the >> “why". >> >> >> The aibility to set up transaction specific redirect URIs is also useful >> in situations where client ids and correspoding credentials and policies >> are managed by a trusted 3rd party, e.g. via client certifiates containing >> client permissions. Such an externally managed client could interact with >> an AS trusting the respective 3rd party without the need for an additional >> registration step. >> >> >> — Justin >> >> On Sep 1, 2020, at 11:05 PM, Takahiko Kawasaki <taka@authlete.com> wrote: >> >> Under existing specifications (RFC 6749, OIDC Core 1.0 and FAPI), a >> client can choose an arbitrary redirect_uri without registering it only >> when all the following conditions are satisfied. >> >> 1. The client type of the client is "confidential". (RFC 6749 Section >> 3.1.2.2 requires that public clients register redirect URIs.) >> 2. The flow is not "implicit". (RFC 6749 Section 3.1.2.2 requires that >> confidential clients utilizing the implicit grant type register redirect >> URIs.) >> 3. The authorization request is not an OIDC request. (OIDC Core 1.0 >> Section 3.1.2.1 requires that redirect_uri match a pre-registered one.) >> 4. The authorization request is not a FAPI request. (FAPI Part 1 Section >> 5.2.2 Clause 8 requires that redirect URIs be pre-registered.) >> >> In short, under existing specifications, pure RFC-6749 >> authorization-code-flow requests from confidential clients can choose an >> arbitrary redirect_uri without registering it. Once OIDC or FAPI is used, >> existing specifications require pre-registration of redirect URIs. I'm not >> sure but if PAR's "redirect_uri Management" is going to introduce rules >> that conflict with existing specifications, it is better to list the >> conflicts explicitly in the section. >> >> Best Regards, >> Takahiko Kawasaki >> >> >> On Wed, Sep 2, 2020 at 3:48 AM Torsten Lodderstedt <torsten= >> 40lodderstedt.net@dmarc.ietf.org> wrote: >> >>> Here is my proposal for the new section: >>> >>> 2.4. redirect_uri Management >>> >>> The OAuth Security BCP [I-D.ietf-oauth-security-topics] as well as OAuth >>> 2.1 [I-D.ietf-oauth-v2-1] require an AS to excactly match the redirect_uri >>> parameter against the set of redirect URIs previously established for a >>> particular client. This is a means to early detect attempts to impersonate >>> a client and prevent token leakage and open redirection. As a downside, it >>> makes client management more complex since the redirect URI is typically >>> the most volatile part of a client policy. >>> >>> This requirement MAY be relaxed by the AS, if a confidential client uses >>> pushed authorization requests since the AS authenticates the client before >>> the authorization process starts and that way ensures it interacts with the >>> legit client. The AS MAY allow such clients to specify redirect_uri values >>> not previously registered with the AS. This will give the client more >>> flexibility (e.g. to mint AS-specific redirect URIs on the fly) and makes >>> client management much easier. It is at the discretion of the AS to apply >>> restriction on redirect_uri values, e.g. the AS MAY require a certain URI >>> prefix or allow only a query parameter to vary at runtime. >>> >>> Note: The aibility to set up transaction specific redirect URIs is also >>> useful in situations where client ids and correspoding credentials and >>> policies are managed by a trusted 3rd party, e.g. via client certifiates >>> containing client permissions. Such an externally managed client could >>> interact with an AS trusting the respective 3rd party without the need for >>> an additional registration step. >>> >>> > On 29. Aug 2020, at 17:22, Justin Richer <jricher@mit.edu> wrote: >>> > >>> > I completely agree with the utility of the function in question here >>> and it needs to be included. I’m in favor of creating a dedicated section >>> for redirect_uri management, so that we can explain exactly how and why to >>> relax the requirement from core OAuth. In addition, I think we want to >>> discuss that the AS might have its own restrictions on which redirect URIs >>> an authenticated client might be able to use. For example, registering a >>> client with a Redirect URI prefix, or allowing only a query parameter to >>> vary at runtime. All of these can be enforced in PAR because the client is >>> presenting its authentication, as you point out, so the AS can determine >>> which policies should apply. >>> > >>> > — Justin >>> > >>> >> On Aug 29, 2020, at 7:52 AM, Torsten Lodderstedt < >>> torsten@lodderstedt.net> wrote: >>> >> >>> >> >>> >>> >>> >>> >>> >>> ¶6: Does the AS really have "the ability to authenticate and >>> authorize clients”? I think what we mean here is "the ability to >>> authenticate clients and validate client requests”, but I’m not positive of >>> the intent. >>> >>> >>> >>> I think the intent is that the AS can check whether a client is >>> authorized to make a particular authorization request (specific scopes, >>> response type, etc.). But checking authorization to request authorization >>> is confusing wording. I think your working is less confusing and still >>> allows for the intent. >>> >>> >>> >>> I'll let Torsten interject if he feels differently as I think he >>> originally wrote the text in question. >>> >> >>> >> that was the original intent. I think “validate" is fine. >>> >> >>> >>> >>> >>> >>> >>> >>> >>> ¶7: I’m not sure I buy this example. Even if the clientID is >>> managed externally, the association with a set or pattern of allowed >>> redirect URIs is still important, and the AS will need to know what that >>> is. I think this example could lead an AS developer to (erroneously and >>> dangerously) conclude that they don’t have to check any other values in a >>> request, including scope and redirect URI. It’s important that DynReg >>> doesn’t alleviate that issue, but removal of DynReg doesn’t really change >>> things in that regard. Suggest removing example or reworking paragraph. >>> >>> >>> >>> I'm going to have to defer to Torsten on this because, to be honest, >>> I'm not too sure about it myself. I tend to lean towards thinking the draft >>> would be better off without it. >>> >>> >>> >> >>> >> In the traditional authorization flow, the redirect_uri serves as way >>> to make sure the AS is really talking to the legit client and the allowed >>> redirect_uri values are determined by the legit client at registration time >>> (might be manually). >>> >> >>> >> With PAR, we have a much stronger means to ensure the AS is talking >>> to the legit client. That’s why I don’t see an issue with letting the >>> client set a per transaction redirect_uri. This will give the client more >>> flexibility (mint AS-specific redirect URIs on the fly) and makes client >>> management much easier since redirect URIs are the most volatile part of a >>> client policy. >>> >> >>> >> It also makes use of OAuth much easier in deployments where client >>> identities are managed by external entities (even without any idea of >>> OAuth). A prominent example is open banking in the EU (aka PSD2). The >>> (technical) identity of any PSD2-licensed client is asserted by an eIDAS >>> compliant CA in a special X.509 certificate. Those certificates contain the >>> permissions (access to account information and/or payment initiation >>> allowed) and the identity (member state specific). But they don’t contain >>> OAuth policy values. Nevertheless, the regulation requires any financial >>> institution in the EU to at runtime, without any registration, to accept >>> and process calls from any licensed PSD2 clients. >>> >> >>> >> There are two ways to cope with it in OAuth context: >>> >> a) use dynamic client registration with the X.509 cert as credential. >>> Unfortunately, RFC 7591 does not support other client authentication means >>> then an initial access token. Beside that, it would violate the text of the >>> regulation. >>> >> b) establish a redirect URL with every transaction. This is the >>> recommended approach in at least one of the PSD2 specs. >>> >> >>> >> PAR is a clean way to solve that problem. >>> >> >>> >> I don’t want this text to cause confusing. On the other hand this >>> potential of PAR is way too important to not mention it at all. What about >>> moving it into a special section "redirect_uri management”? >>> >> >>> >>> >>> >> >>> > >>> >>> _______________________________________________ >>> OAuth mailing list >>> OAuth@ietf.org >>> https://www.ietf.org/mailman/listinfo/oauth >>> >> >> > *CONFIDENTIALITY NOTICE: This email may contain confidential and > privileged material for the sole use of the intended recipient(s). Any > review, use, distribution or disclosure by others is strictly prohibited. > If you have received this communication in error, please notify the sender > immediately by e-mail and delete the message and any file attachments from > your computer. 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- [OAUTH-WG] WGLC Review of PAR Justin Richer
- Re: [OAUTH-WG] WGLC Review of PAR Brian Campbell
- Re: [OAUTH-WG] WGLC Review of PAR Justin Richer
- Re: [OAUTH-WG] WGLC Review of PAR Brian Campbell
- Re: [OAUTH-WG] WGLC Review of PAR Dick Hardt
- Re: [OAUTH-WG] WGLC Review of PAR Justin Richer
- Re: [OAUTH-WG] WGLC Review of PAR Dick Hardt
- Re: [OAUTH-WG] WGLC Review of PAR Torsten Lodderstedt
- Re: [OAUTH-WG] WGLC Review of PAR Torsten Lodderstedt
- Re: [OAUTH-WG] WGLC Review of PAR Justin Richer
- Re: [OAUTH-WG] WGLC Review of PAR Torsten Lodderstedt
- Re: [OAUTH-WG] WGLC Review of PAR Dick Hardt
- Re: [OAUTH-WG] WGLC Review of PAR Brian Campbell
- Re: [OAUTH-WG] WGLC Review of PAR Torsten Lodderstedt
- Re: [OAUTH-WG] WGLC Review of PAR Takahiko Kawasaki
- Re: [OAUTH-WG] WGLC Review of PAR Justin Richer
- Re: [OAUTH-WG] WGLC Review of PAR Brian Campbell
- Re: [OAUTH-WG] WGLC Review of PAR Justin Richer
- Re: [OAUTH-WG] WGLC Review of PAR Torsten Lodderstedt
- Re: [OAUTH-WG] WGLC Review of PAR Brian Campbell
- Re: [OAUTH-WG] WGLC Review of PAR Dave Tonge
- Re: [OAUTH-WG] WGLC Review of PAR Torsten Lodderstedt
- Re: [OAUTH-WG] WGLC Review of PAR Torsten Lodderstedt