This is an excellent security point. I also imagine that in "federated" cases an RS could have its own subject scheme / namespace, distinct from the one at the AS, including for clients acting on their own behalf.
Vladimir On 07/05/2019 11:37, Neil Madden wrote: > I wasn’t at IIW so I may be missing some context. > > There is a potential security issue if the client_id is used as the “sub” for > an AT obtained via client_credentials. If the client can register itself with > a self-chosen client_id then it may deliberately chose a client_id that > matches the user name of a privileged user. An RS that just blindly looks at > the “sub” claim may then erroneously let the client perform privileged > actions. > > Is this the context of the discussion? > > Given that there are a lot of RSes in existence, many of which are probably > just looking at the “sub” claim to identify the resource owner, I think the > onus is on the AS to ensure that no such ambiguity can arise in the first > place by ensuring that the space of “sub” values for client credentials is > disjoint with the space for genuine users or by disallowing the > client_credentials grant altogether. > > This issue already arises in token introspection though, so maybe ought to be > mentioned in the OAuth security topics draft rather than specific to the JWT > AT draft? > > — Neil > >> On 6 May 2019, at 18:32, Vittorio Bertocci >> <Vittorio=40auth0....@dmarc.ietf.org> wrote: >> >> Hi all, >> thanks for your patience during this month long hiatus, and thanks for the >> comments. >> Last week at IIW I had the opportunity to discuss this with many of the >> people on the list. Here's a summary of where the discussion landaed on the >> subject of the sub (pun intended). >> >> - It seems that RFC 7519 has pretty clear language on the use of sub- I >> didn't check it back when we started the discussion. I do agree with the >> people saying that we shouldn't violate existing specifications, hence it >> looks like we do need to have sub also in the case in which we have app-only >> tokens carrying claims about the app itself. I understand this will cause >> some implementation to break, but unfortunately that's intrinsic in the >> process of coming up with a common approach and standards compliance is >> probably one of the strongest reasons to tolerate that. >> - That said, I am strongly committed to preserve existing functionality. One >> of the main reasons that was brought up for including sub only for user >> based ATs was to use it as heuristic for telling those tokens apart from >> app-only ones. To that end, Karl MCGuinness suggested that we include >> grant_type as a return claim, which the RS could use to the same effect. I >> find the proposal very clever, and the people at IIW thought so as well. >> What you think? >> Note, John Bradley observed that in some cases this might lead to ambiguous >> results if an extension grant is used (say an assertion profile) but that >> seems like a relatively fringe occurrence. >> >> On Thu, Apr 4, 2019 at 1:11 PM Hans Zandbelt <hans.zandb...@zmartzone.eu >> <mailto:hans.zandb...@zmartzone.eu>> wrote: >> I also meant to say that (of course) the JWT standard doesn't say that the >> JWT is supposed to be about the client or about the resource owner, hence >> both are valid >> >> Hans. >> >> On Thu, Apr 4, 2019 at 10:09 PM Mike Jones <michael.jo...@microsoft.com >> <mailto:michael.jo...@microsoft.com>> wrote: >> I get that existing practice is likely to be all over the map, but if we’re >> to create a JWT access token standard, it’s reasonable to require that the >> claims usage comply with the JWT standards. >> >> >> >> -- Mike >> >> >> >> From: Hans Zandbelt <hans.zandb...@zmartzone.eu >> <mailto:hans.zandb...@zmartzone.eu>> >> Sent: Thursday, April 4, 2019 12:59 PM >> To: Mike Jones <michael.jo...@microsoft.com >> <mailto:michael.jo...@microsoft.com>> >> Cc: George Fletcher <gffletch=40aol....@dmarc.ietf.org >> <mailto:40aol....@dmarc...ietf.org>>; Vittorio Bertocci >> <Vittorio=40auth0....@dmarc.ietf.org <mailto:40auth0....@dmarc.ietf.org>>; >> IETF oauth WG <oauth@ietf.org <mailto:oauth@ietf.org>> >> Subject: Re: [OAUTH-WG] draft-bertocci-oauth-access-token-jwt-00 >> >> >> >> the definition of RFC 7519 is actually "petitio principii" and a lot of >> deployments put claims about the Resource Owner in the access token (as a >> Resource Server implementer I've suffered a lot from this) >> >> >> >> Hans. >> >> >> >> On Thu, Apr 4, 2019 at 9:48 PM Mike Jones <michael.jo...@microsoft.com >> <mailto:michael.jo...@microsoft.com>> wrote: >> >> I agree with George that the subject of a token must be the principal of >> that token. That what the JWT “sub” claim is for. Indeed, the first >> sentence of the “sub” definition at >> https://tools.ietf.org/html/rfc7519#section-4.1.2 >> <https://tools.ietf.org/html/rfc7519#section-4.1.2> is: >> >> The "sub" (subject) claim identifies the principal that is the subject of >> the JWT. >> >> >> >> If an access token uses “sub”, its usage must comply with the definition >> from RFC 7519. >> >> >> >> -- Mike >> >> >> >> From: OAuth <oauth-boun...@ietf.org <mailto:oauth-boun...@ietf.org>> On >> Behalf Of George Fletcher >> Sent: Thursday, April 4, 2019 8:51 AM >> To: Hans Zandbelt <hans.zandb...@zmartzone.eu >> <mailto:hans.zandb...@zmartzone.eu>> >> Cc: Vittorio Bertocci <Vittorio=40auth0....@dmarc.ietf.org >> <mailto:40auth0....@dmarc.ietf.org>>; IETF oauth WG <oauth@ietf.org >> <mailto:oauth@ietf.org>> >> Subject: Re: [OAUTH-WG] draft-bertocci-oauth-access-token-jwt-00 >> >> >> >> The more I think about this the more I land in the "No" camp. >> >> The subject of a token should be the principal of that token. It shouldn't >> matter whether that is a machine, a user, or a device. Trying to separate >> out "humans" as a special class will just make things more complicated. If >> we need a claim to identify the subject is a "human" then why not just add >> that. This doesn't break anything and makes it easy for people to detect >> this case in those use cases where it's required. >> >> Thanks, >> George >> >> On 4/3/19 4:56 PM, Hans Zandbelt wrote: >> >> I will argue that in a way such deployments are already broken e.g. in the >> typical use case of onboarding client accounts in the same >> directory/OU/namespace as user accounts and we don't need to cater for that. >> >> >> >> Hans. >> >> >> >> On Wed, Apr 3, 2019 at 10:48 PM George Fletcher <gffle...@aol.com >> <mailto:gffle...@aol.com>> wrote: >> >> I agree that this will break a lot of existing flows... especially those >> using any form of the client_credentials flow. In that sense I'm not >> completely on board yet :) >> >> On 3/26/19 12:56 PM, Hans Zandbelt wrote: >> >> great summary! this will hurt quite a few existing m2m deployments but I do >> like the rigidness of it all: it is very explicit, cannot misinterpreted and >> thus prevents failure (which is really what Dominick is after); I'm on board >> >> >> >> Hans. >> >> >> >> On Tue, Mar 26, 2019 at 5:49 PM Vittorio Bertocci >> <Vittorio=40auth0....@dmarc.ietf.org <mailto:40auth0....@dmarc.ietf.org>> >> wrote: >> >> thank you Steinar and everyone else for the comments on this! >> >> To summarize the situation so far: Dominick, Steinar, Rob, David, Nov, >> Bertrand recommend using sub only for users. Martin would like to have the >> sub for app only flows as well. Hans is neutral. >> >> That does sound like the sub as user has more consensus, tho before changing >> it I'd wait for the people currently at IETF104 to have more time to comment >> as well. >> >> Clarification. If the goal is to be able to apply the logic "if there's a >> sub, it's a user flow", we have to explicitly disallow (MUST NOT) the use of >> sub when that's not the case. Are all OK with it? >> >> >> >> Dave, the suggestion of having explicit typing for app only vs user only is >> interesting! For the purpose of putting together an interoperable profile, >> tho, I would suggest we table it for v1 in the interest of getting to >> something easy to adopt (hence with small delta vs existing implementations) >> faster. >> >> >> >> On Tue, Mar 26, 2019 at 1:40 AM Steinar Noem <stei...@udelt.no >> <mailto:stei...@udelt.no>> wrote: >> >> Hi Vittorio, we (the national federation-gateway for the health services in >> norway - "HelseID") think his is a really valuable initiative! >> >> We also agree with Dominick concerning definition of the "sub" claim. >> >> >> >> <mvh>Steinar</mvh> >> >> >> >> tir. 26. mar. 2019 kl. 07:25 skrev Dominick Baier <dba...@leastprivilege.com >> <mailto:dba...@leastprivilege.com>>: >> >> From an access token consumer (aka API) developer point of view, I prefer >> this logic >> >> >> >> "If sub is present - client acts on behalf of a user, if not - not." >> >> >> >> Anything more complicated has a potential of going wrong. >> >> >> >> On 26. March 2019 at 01:34:53, Nov Matake (mat...@gmail.com >> <mailto:mat...@gmail.com>) wrote: >> >> Hi Vittorio, >> >> >> >> Yeah, I’m concerning user & client ids collision. >> >> I haven’t seen such implementations, but user-select username as sub, or >> incremental integer as sub & client_id will be easily collide. >> >> >> >> If you can enforce collision resistant IDs between user & client instances, >> it’ll works fine. I feel its overkill though. >> >> >> >> Sent from my iPhone >> >> >> On Mar 26, 2019, at 8:51, Vittorio Bertocci <vitto...@auth0.com >> <mailto:vitto...@auth0.com>> wrote: >> >> Hey Nov, Dominick, Hans- >> >> thanks for the comments. That was an area I was expecting to cause more >> discussion, and I am glad we are having this opportunity to clarify. >> >> The current language in the draft traces the etymology of sub to OpenID >> Connect core, hence Dominick observation is on point. However in the >> description I express something in line with 7519, which was in fact my >> intent. >> >> >> >> The idea was to provide an identifier of the calling subject that is >> guaranteed to be present in all cases- this would allow an SDK developer to >> use the same code for things like lookups and membership checks regardless >> of the nature of the caller (user in a delegated case, app in app-only >> grants). The information to discriminate between user and app callers is >> always available in the token (say, the caller is a user if sub!=client_id, >> where client_id is always guaranteed to be present as well) hence there's no >> loss in expressive power, should that difference be relevant for the >> resource server. >> >> >> >> Dominick, Hans- I probably missed the security issue you guys are thinking >> of in this case. Of course, if this would introduce a risk I completely >> agree it should be changed- I'd just like to understand better the problem. >> Could you expand it in a scenario/use case to clarify the risk? >> >> Nov- playing this back: is the concern that a user and a client might have >> the same identifier within an IDP? When using collision resistant IDs, as it >> is usually the case, that seems to be a remote possibility- did you stumble >> in such scenario in production? >> >> >> >> Thanks >> >> V. >> >> >> >> >> >> On Mon, Mar 25, 2019 at 7:44 AM Hans Zandbelt <hans.zandb...@zmartzone.eu >> <mailto:hans.zandb...@zmartzone.eu>> wrote: >> >> I believe there are plenty of OAuth 2.0 only use cases out there... but >> nevertheless I agree with the potential confusion and thus security problems >> arising from that (though one may argue the semantics are the same). >> >> >> >> Hans. >> >> >> >> On Mon, Mar 25, 2019 at 3:39 PM Dominick Baier <dba...@leastprivilege.com >> <mailto:dba...@leastprivilege.com>> wrote: >> >> Yes I know - and I think in hindsight it was a mistake to use the same claim >> type for multiple semantics. >> >> >> >> All the “this is OIDC not OAuth” arguments are making things more >> complicated than they need to be - in my experience almost no-one (that I >> know) does OIDC only - nor OAuth only. They always combine it. >> >> >> >> In reality this leads to potential security problems - this spec has the >> potential to rectify the situation. >> >> >> >> Dominick >> >> On 25. March 2019 at 14:58:56, Hans Zandbelt (hans.zandb...@zmartzone.eu >> <mailto:hans.zandb...@zmartzone.eu>) wrote: >> >> Without agreeing or disagreeing: OIDC does not apply here since it is not >> OAuth and an access token is not an id_token. >> >> The JWT spec says in https://tools.ietf.org/html/rfc7519#section-4.1.2 >> <https://tools.ietf.org/html/rfc7519#section-4.1.2>: >> >> >> >> "The "sub" (subject) claim identifies the principal that is the >> >> subject of the JWT. The claims in a JWT are normally statements >> >> about the subject. The subject value MUST either be scoped to be >> >> locally unique in the context of the issuer or be globally unique. >> >> The processing of this claim is generally application specific" >> >> >> >> which kind of spells "client" in case of the client credentials grant but I >> also do worry about Resource Servers thinking/acting only in terms of users >> >> >> >> Hans. >> >> >> >> On Mon, Mar 25, 2019 at 2:41 PM Dominick Baier <dba...@leastprivilege.com >> <mailto:dba...@leastprivilege.com>> wrote: >> >> IMHO the sub claim should always refer to the user - and nothing else. >> >> >> >> OIDC says: >> >> >> >> "Subject - Identifier for the End-User at the Issuer." >> >> >> >> client_id should be used to identify clients. >> >> >> >> cheers >> >> Dominick >> >> >> >> On 25.. March 2019 at 05:13:03, Nov Matake (mat...@gmail.com >> <mailto:mat...@gmail.com>) wrote: >> >> Hi Vittorio, >> >> >> >> Thanks for the good starting point of standardizing JWT-ized AT. >> >> >> >> One feedback. >> >> The “sub” claim can include 2 types of identifier, end-user and client, in >> this spec. >> >> It requires those 2 types of identifiers to be unique each other in the IdP >> context. >> >> >> >> I prefer omitting “sub” claim in 2-legged context, so that no such >> constraint needed. >> >> >> >> thanks >> >> >> >> nov >> >> >> >> On Mar 25, 2019, at 8:29, Vittorio Bertocci >> <vittorio.bertocci=40auth0....@dmarc.ietf.org >> <mailto:vittorio.bertocci=40auth0....@dmarc.ietf.org>> wrote: >> >> >> >> Dear all, >> >> I just submitted a draft describing a JWT profile for OAuth 2.0 access >> tokens. You can find it in >> https://datatracker.ietf.org/doc/draft-bertocci-oauth-access-token-jwt/ >> <https://datatracker.ietf.org/doc/draft-bertocci-oauth-access-token-jwt/>. >> >> I have a slot to discuss this tomorrow at IETF 104 (I'll be presenting >> remotely). I look forward for your comments! >> >> >> >> Here's just a bit of backstory, in case you are interested in how this doc >> came to be. The trajectory it followed is somewhat unusual. >> >> Despite OAuth2 not requiring any specific format for ATs, through the years >> I have come across multiple proprietary solution using JWT for their access >> token. The intent and scenarios addressed by those solutions are mostly the >> same across vendors, but the syntax and interpretations in the >> implementations are different enough to prevent developers from reusing code >> and skills when moving from product to product. >> I asked several individuals from key products and services to share with me >> concrete examples of their JWT access tokens (THANK YOU Dominick Baier >> (IdentityServer), Brian Campbell (PingIdentity), Daniel Dobalian >> (Microsoft), Karl Guinness (Okta) for the tokens and explanations!). >> I studied and compared all those instances, identifying commonalities and >> differences. >> I put together a presentation summarizing my findings and suggesting a rough >> interoperable profile >> (slides:https://sec.uni-stuttgart.de/_media/events/osw2019/slides/bertocci_-_a_jwt_profile_for_ats.pptx >> >> <https://sec..uni-stuttgart.de/_media/events/osw2019/slides/bertocci_-_a_jwt_profile_for_ats.pptx> >> ) - got early feedback from Filip Skokan on it. Thx Filip! >> The presentation was followed up by 1.5 hours of unconference discussion, >> which was incredibly valuable to get tight-loop feedback and incorporate new >> ideas. John Bradley, Brian Campbell Vladimir Dzhuvinov, Torsten Lodderstedt, >> Nat Sakimura, Hannes Tschofenig were all there and contributed generously to >> the discussion. Thank you!!! >> Note: if you were at OSW2019, participated in the discussion and didn't get >> credited in the draft, my apologies: please send me a note and I'll make >> things right at the next update. >> On my flight back I did my best to incorporate all the ideas and feedback in >> a draft, which will be discussed at IETF104 tomorrow. Rifaat, Hannes and >> above all Brian were all super helpful in negotiating the mysterious syntax >> of the RFC format and submission process. >> I was blown away by the availability, involvement and willingness to invest >> time to get things right that everyone demonstrated in the process. This is >> an amazing community. >> >> V. >> >> _______________________________________________ >> OAuth mailing list >> OAuth@ietf.org <mailto:OAuth@ietf.org> >> https://www.ietf.org/mailman/listinfo/oauth >> <https://www.ietf.org/mailman/listinfo/oauth> >> >> >> _______________________________________________ >> OAuth mailing list >> OAuth@ietf.org <mailto:OAuth@ietf.org> >> https://www.ietf.org/mailman/listinfo/oauth >> <https://www.ietf.org/mailman/listinfo/oauth> >> _______________________________________________ >> OAuth mailing list >> OAuth@ietf.org <mailto:OAuth@ietf.org> >> https://www.ietf.org/mailman/listinfo/oauth >> <https://www.ietf.org/mailman/listinfo/oauth> >> >> >> >> -- >> >> hans.zandb...@zmartzone.eu <mailto:hans.zandb...@zmartzone.eu> >> ZmartZone IAM - www.zmartzone.eu <http://www.zmartzone.eu/> >> >> >> >> -- >> >> hans.zandb...@zmartzone.eu <mailto:hans.zandb...@zmartzone.eu> >> ZmartZone IAM - www.zmartzone.eu <http://www.zmartzone.eu/> >> _______________________________________________ >> OAuth mailing list >> OAuth@ietf.org <mailto:OAuth@ietf.org> >> https://www.ietf.org/mailman/listinfo/oauth >> <https://www.ietf.org/mailman/listinfo/oauth> >> >> >> >> -- >> >> Vennlig hilsen >> >> >> >> Steinar Noem >> >> Partner Udelt AS >> >> Systemutvikler >> >> >> >> | stei...@udelt.no <mailto:stei...@udelt..no> | h...@udelt.no >> <mailto:h...@udelt.no> | +47 955 21 620 | www.udelt.no >> <http://www.udelt.no/> | >> >> _______________________________________________ >> OAuth mailing list >> OAuth@ietf.org <mailto:OAuth@ietf.org> >> https://www.ietf.org/mailman/listinfo/oauth >> <https://www.ietf.org/mailman/listinfo/oauth> >> >> >> >> -- >> >> hans.zandb...@zmartzone.eu <mailto:hans.zandb...@zmartzone.eu> >> ZmartZone IAM - www.zmartzone.eu <http://www.zmartzone.eu/> >> >> >> _______________________________________________ >> OAuth mailing list >> OAuth@ietf.org <mailto:OAuth@ietf.org> >> https://www.ietf.org/mailman/listinfo/oauth >> <https://www.ietf.org/mailman/listinfo/oauth> >> >> >> >> >> >> >> -- >> >> hans.zandb...@zmartzone.eu <mailto:hans.zandb...@zmartzone.eu> >> ZmartZone IAM - www.zmartzone.eu <http://www.zmartzone.eu/> >> >> >> >> >> >> >> -- >> >> hans.zandb...@zmartzone.eu <mailto:hans.zandb...@zmartzone.eu> >> ZmartZone IAM - www.zmartzone.eu <http://www.zmartzone.eu/> >> >> -- >> hans.zandb...@zmartzone.eu <mailto:hans.zandb...@zmartzone.eu> >> ZmartZone IAM - www.zmartzone.eu <http://www.zmartzone.eu/> >> _______________________________________________ >> 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
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