We had two mandates. One was to provide a spec for AS metadata. The other was to mitigate the client mixup attack. The request was to do the latter without requiring the former for clients that don’t otherwise need discovery.
Returning the issuer and client_id from the authorization endpoint and the client checking them can be done by the client without discovery. Any client that has the resource and issuer hard coded probably doesn’t need discovery. One of the things that a client will need discovery for is to find the RS, so requiring the client to know the RS URI before getting the AS config seems backwards to me. Unless the client tells the AS where it intends to use the token we will be leaving a security hole because the bearer tokens will have too loose an audience if they have one at all. True you are telling the AS (Webfinger service) what the RS is but that is not at a place that is useful in the token production process. I also think there are use cases where the AS doesn’t know all the possible RS. That is not something that a out of band check can address. There are also cases where a token might be good at multiple RS endpoints intentionally. In your solution the client would need to make a discovery request for each endpoint. Those requests lack the context of who the client and resource owner are. I think that will be a problem in some use cases. If this is added to the token endpoint it would be checked when code or refresh are exchanged, not every time the token is used. With a out of band check the client would never know if a RS was removed/revoked. I don’t see checking when refreshing a token as something that is a huge burden. If the server wants to do the check on it’s side then we could require the client to send the RS URI in the token request. that way you really know the client is not going to get a token for the wrong RS endpoint. If you check out of band in discovery you really have no idea if the client is checking. John B. > On Mar 14, 2016, at 3:56 PM, Phil Hunt <phil.h...@oracle.com> wrote: > > Thanks to Mike and John for their feedback. I’ll take each in turn: > > Mike, > > Regarding your suggested amendments > > Item 1: Returning the config URL would create two problems. One,it makes > bound discovery a two-step process - that adds complexity. It seems far > simpler to mandate TLS (which I think it already does in the security > considerations). > > The two-step process allows the current discovery process to continue. I > disagree with this. This is why I put forward an “alternate" draft that is > almost the same but simply adds the check before returning the configuration > data. I worry that developers would have no incentive to do the two-step > approach. They would just start at step 2 which in turn puts AS’s at risk of > exposing tokens because it works. This makes OAuth promiscuous. > > Regarding existing implementations. Most of those implementations are for > OIDC. I think it makes sense for OIDF to continue use of OIDC's discovery > spec because the UserInfo endpoint is well defined and the likelihood of a > client mis-informed about the resource endpoint is not there. IMO This does > not apply to the broader OAuth community. > > Item 2: It may be appropriate to have a separate configuration registry > specification, but I think we should hold off until we have a complete > solution and then make the decision what drafts should exist and how many > pieces. A big concern is the perceived complexity of multiple solutions and > multiple drafts. > > As to John Bradley’s comments: > > Re: Discovery is the wrong place to mitigate threats. > I’m confused by this. Our mandate was to solve a security threat by having a > discovery specification to prevent clients being mis-lead about endpoints (of > which resource service is one) in an oauth protected exchange. Maybe what > you mean is we should not use .well-known of any kind and we should just > create a “/Config” endpoint to OAuth? > > Re: Your proposal for MITM mitigation > You propose that instead the resource endpoint check should be in the oauth > protocol itself. The difference is that validation is transferred back to > the client to get it right. As well, without the client informing the AS, I > can’t see a way for the AS to know what endpoint the client is using. The > webfinger approach does this once and only requires that the host name be > checked in many cases. > > As a principle, the members have discussed many times that the AS service > should do validation when possible — this was particularly true at the > Germany meeting when this came up. This is why I prefer the client tell the > service provider what it intends to do and the service provider can fail that > request immediately if necessary. We don’t have to depend on the developer > getting the spec correct to fail the correct way. > > I worry that adding more parameters to the authz and token protocol flows > increases complexity and attack surface. It also means per authorization > validation has to take place vs. a one-time validation at config time. > Placing it in the configuration lookup phase (whether via web finger or just > a special OAuth endpoint) seems more appropriate and far less complex - as > the request itself is simple and has only one parameter. Here we are not > considered about legitimacy of the client. we’re just concerned with the > issue "has the client been correctly informed?” > > That said, it may be that when we consider all the use cases, some > combination of AS protocol and discovery may be both needed. I’m not ready to > make conclusions about this. The current oauth-discovery spec seems to put > future generic clients at risk and that is my primary concern. > > Best Regards, > > Phil > > @independentid > www.independentid.com <http://www.independentid.com/>phil.h...@oracle.com > <mailto:phil.h...@oracle.com> > > > > > >> On Mar 13, 2016, at 10:28 PM, Mike Jones <michael.jo...@microsoft.com >> <mailto:michael.jo...@microsoft.com>> wrote: >> >> Thanks for posting this, Phil. It provides a concrete example of a way that >> protected resource discovery could be added to authorization server metadata >> discovery, and as such, should provide useful input for working group >> discussions on this topic. It’s always great when someone takes the time to >> write an actual draft that can be examined and implemented, and I appreciate >> you doing that. >> >> The content of your draft points out that there appears to be complete >> agreement on what the authorization server metadata format should be, which >> is great! I’ll note that Section 3 of draft-hunt-oauth-bound-config-00 >> titled “Authorization Server Metadata” is an exact copy of Section 2 of >> draft-ietf-oauth-discovery-01 (with the same title), modulo applying a >> correction suggested by the working group. To me this suggests that the >> authorization server metadata definitions in draft-ietf-oauth-discovery >> (which is now the whole normative content of the draft) are clearly ready >> for standardization, since even your alternative proposal includes them >> verbatim. >> >> Reading your draft, the problem I have with it is that you are returning the >> AS metadata only as a WebFinger response, rather than as an https-protected >> resource published by the authorization server. The choice to only return >> this via WebFinger makes your draft incompatible with most deployed >> implementations of OAuth metadata, including the 22 implementations using it >> listed athttp://openid.net/certification/ <http://openid.net/certification/> >> (see the “OP Config” column in the table) and OAuth 2.0 libraries such as >> Microsoft’s “ADAL” library, which uses the metadata path for client >> configuration. Without having ASs provide the metadata as an >> https-protected resource, implementations such as ADAL can’t use it for >> client configuration as the currently do. <> >> >> Therefore, I would request that you make these minor revisions to your draft >> and republish, so as to provide a unified way forward that is compatible >> with all known existing OAuth Discovery deployments: >> 1. Modify your section 2 “Authorization Server WebFinger Discovery” to >> have the WebFinger request return the issuer identifier for the AS as the >> “WebFinger “rel” value, rather than returning the metadata values by value >> as the “properties” value. >> 2. Reference the metadata definitions from Section 2 of >> draft-ietf-oauth-discovery, rather than duplicating them in your Section 3. >> >> That would have the advantage of paring your draft down to only the new >> things that it proposes, enabling them to be more clearly understood and >> evaluated on their own merits. I look forward to the discussions of ways of >> performing additional kinds of OAuth discovery, and consider your draft a >> valuable input to those discussions. >> >> Best wishes, >> -- Mike >> >> From: OAuth [mailto:oauth-boun...@ietf.org <mailto:oauth-boun...@ietf.org>] >> On Behalf Of John Bradley >> Sent: Sunday, March 13, 2016 6:45 PM >> To: Phil Hunt <phil.h...@oracle.com <mailto:phil.h...@oracle.com>> >> Cc: oauth <oauth@ietf.org <mailto:oauth@ietf.org>> >> Subject: Re: [OAUTH-WG] New Version Notification for >> draft-hunt-oauth-bound-config-00.txt >> >> As I have told Phil off list. >> >> Discovery is the wrong place to try and provide security against man in the >> middle attacks on the RS. >> >> This requires the client to know what the RS URI is before retrieving the >> information on the AS Configuration. >> >> The proposal Mike and I have been working on requires the client to have a >> notion of what API it is looking for and retrieve the .well-known file for >> that API from the issuer. That allows a protocol like Connect to register >> its own config file that can point to the RS. >> >> If the API specific well known is not available the client can try the >> default oauth-server one. >> >> That then allows us to deal with restricting where AT are presented as part >> of the protocol rather then dragging discovery in as a requirement. >> >> In my opinion the resource the token is targeted to should be separated from >> the scope and returned as part of the meta-data about the AT along with >> scopes granted and expiry time. We should also have a input parameter for >> resources so that a client can restrict tokens issued to a subset of the >> ones granted by the refresh token. It would then also be possible to ask a >> AS for a token for a unregistered RS and have the AS produce a JWT access >> token with the resource as an audience if policy allows. >> >> That however was supposed to be dealt with as part of the mixed up client >> set of mitigations. >> In that the goal was to mitigate the attacks by returning meta-data about >> the tokens, and not to require discovery. >> >> We intend to return “iss” and “cleint_id” for the code, and I intend to >> discuss at the F2F returning resource for AT as well. >> >> Those mitigate the attack. >> >> I will continue to resist mixing up discovery of configuration meta-data >> with mitigation of the attacks. >> >> We return meta-data about the tokens now, because AT are opaque to the >> client, we neglected to include some of the information for the client needs >> to be secure. We just need to add that in to the existing flows. >> >> While Phil’s proposal is easier for the AS to implement as an add on, it >> puts more of a burden on the client needing to potentially change how it >> stores the relationships between AS and RS to prevent compromise, I think >> the solution should be biased towards simplicity on the client side. >> >> If we return the resources as part of the existing meta data the client >> checks that against the resource it intends to send the token to and if it >> is not in the list then it can’t send the token. Simple check every time it >> gets a new AT, no optionality. >> >> I am not saying anything new Nat has been advocating basically this for some >> time, and dis submit a draft. I prefer to return the info in the existing >> format rather than as link headers, but that is the largest difference >> between what Nat and I are saying with respect to resource. >> >> That is the core of my problem with Phil’s draft. >> >> I guess we will need to have a long conversation in BA. >> >> Regards >> John B. >> >> On Mar 13, 2016, at 8:12 PM, Phil Hunt <phil.h...@oracle.com >> <mailto:phil.h...@oracle.com>> wrote: >> >> This draft is a proposed alternate proposal for draft-ietf-oauth-discovery. >> As such, it contains the same registry for OAuth Config Metadata as the >> authors believe that both solutions are not required, or depending on WG >> discussion they will be merged. The intent is to provide a simple complete >> draft for consideration. >> >> How it works... >> Given that a client has previously discovered an OAuth protected resource, >> the bound configuration method allows a client to return the configuration >> for an oauth authorization server that can issue tokens for the resource URI >> specified by the client. The AS is not required to be in the same domain. >> The AS is however required to know if it can issue tokens for a resource >> service (which presumes some agreement exists on tokens etc). >> >> The draft does not require that the resource exist (e.g. for unconfigured or >> new user based resources). It only requires that the AS service provider >> agrees it can issue tokens. >> >> From a security perspective, returning the OAuth service configuration for a >> specified resource URI serves to confirm the client is in possession of a >> valid resource URI ensuring the client has received a valid set of endpoints >> for the resource and the associated oauth services. >> >> I propose that the WG consider the alternate draft carefully as well as >> other submissions and evaluate the broader discovery problem before >> proceeding with WGLC on OAuth Discovery. >> >> Thanks! >> >> Phil >> >> @independentid >> www.independentid.com <http://www.independentid.com/> >> phil.h...@oracle.com <mailto:phil.h...@oracle.com> >> >> >> >> Begin forwarded message: >> >> From: internet-dra...@ietf.org <mailto:internet-dra...@ietf.org> >> Subject: New Version Notification for draft-hunt-oauth-bound-config-00.txt >> Date: March 13, 2016 at 3:53:37 PM PDT >> To: "Phil Hunt" <phil.h...@yahoo.com <mailto:phil.h...@yahoo.com>>, "Anthony >> Nadalin" <tony...@microsoft.com <mailto:tony...@microsoft.com>>, "Tony >> Nadalin" <tony...@microsoft.com <mailto:tony...@microsoft.com>> >> >> >> A new version of I-D, draft-hunt-oauth-bound-config-00.txt >> has been successfully submitted by Phil Hunt and posted to the >> IETF repository. >> >> Name: draft-hunt-oauth-bound-config >> Revision: 00 >> Title: OAuth 2.0 Bound Configuration Lookup >> Document date: 2016-03-13 >> Group: Individual Submission >> Pages: 22 >> URL: >> https://www.ietf.org/internet-drafts/draft-hunt-oauth-bound-config-00.txt >> <https://www.ietf.org/internet-drafts/draft-hunt-oauth-bound-config-00.txt> >> Status: >> https://datatracker.ietf.org/doc/draft-hunt-oauth-bound-config/ >> <https://datatracker.ietf.org/doc/draft-hunt-oauth-bound-config/> >> Htmlized: https://tools.ietf.org/html/draft-hunt-oauth-bound-config-00 >> <https://tools.ietf.org/html/draft-hunt-oauth-bound-config-00> >> >> >> Abstract: >> This specification defines a mechanism for the client of an OAuth 2.0 >> protected resource service to obtain the configuration details of an >> OAuth 2.0 authorization server that is capable of authorizing access >> to a specific resource service. The information includes the OAuth >> 2.0 component endpoint location URIs and as well as authorization >> server capabilities. >> >> >> >> >> Please note that it may take a couple of minutes from the time of submission >> until the htmlized version and diff are available at tools.ietf.org >> <http://tools.ietf.org/>. >> >> The IETF Secretariat >> >> >> _______________________________________________ >> OAuth mailing list >> OAuth@ietf.org <mailto:OAuth@ietf.org> >> https://www.ietf.org/mailman/listinfo/oauth >> <https://www.ietf.org/mailman/listinfo/oauth>
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