I implemented the draft quickly and found no big hurdle for authorization server implementations. The current snapshot of my implementation does not add the `iss` parameter when JARM is used. However, for interoperability, I feel that the spec should describe expected behaviors when a JWT is included in an authorization response. The following is an implementer's comment for some cases.
Case 1: When JARM is used An `iss` claim is included in the response JWT as one of top-level entries together with response parameters. It is not so unnatural to regard the `iss` claim as a response parameter. Conclusion would be "When JARM is used, the `iss` parameter is not necessary." Case 2: When an ID token is issued It is unnatural to regard the `iss` claim in an ID token as a response parameter. However, because FAPI Part 2 has already been using an ID token as detached signature for integrity protection, it would be difficult to find a convincing reason to prohibit using the `iss` claim in an ID token as a countermeasure to mix-up attacks. Conclusion would be "When an ID token is issued, the `iss` parameter is not necessary." Case 3: When an unencrypted JWT access token is issued It is technically possible to use the `iss` claim in an unencrypted JWT access token as the `iss` parameter. However, requiring the client to check the `iss` claim means "The access token is no longer opaque to the client." Conclusion would be "Even when an access token is issued and its format is JWT, the `iss` parameter is necessary." BTW, I found that a certain system raises an error when an unknown response parameter (that is, the `iss` parameter) is included in error authorization responses. To ask the administrator of the system to regard the `iss` parameter as a known one, at least the spec draft needs to be adopted by the community as a working draft. I hope that "call for adoption" for the draft will be conducted soon. Best Regards, Taka On Wed, Nov 4, 2020 at 4:46 AM Takahiko Kawasaki <t...@authlete.com> wrote: > It sounds that the Security Considerations section or somewhere > appropriate should have a paragraph like below. > > When an authorization response includes a JWT whose `iss` claim represents > the issuer identifier of the authorization server, the `iss` claim can be > used as a substitute for the `iss` parameter. Therefore, such authorization > response does not have to have the `iss` parameter outside the JWT > separately. Examples of such JWTs include the value of the `id_token` > parameter in OIDC and the value of `response` parameter in JARM. > > Taka > > On Tue, Nov 3, 2020 at 10:46 PM Joseph Heenan <jos...@authlete.com> wrote: > >> I agree, it is in redundant in the JARM case. >> >> I find the text in >> https://www.ietf.org/archive/id/draft-meyerzuselhausen-oauth-iss-auth-resp-01.html#name-security-considerations >> (the 4th paragraph where JARM & JWTs) are mentioned a bit confusing - I >> think it would be good to say something along the lines of: >> >> Although integrity protection is not necessary to prevent mixup, any >> authorization response method that includes a JWT with an ‘iss' (for >> example, JARM or OIDC hybrid flow) will prevent the attack (assuming the >> client is validating the iss). >> >> >> I’m not entirely sure I understand what "MUST NOT allow multiple >> authorization servers to return the same issuer identifier during >> registration” means as I don’t think https://tools.ietf.org/html/rfc7591 >> returns the issuer? >> >> It might be clearer to say something like “When >> https://tools.ietf.org/html/rfc8414 is used the client MUST implement >> the validation described in >> https://tools.ietf.org/html/rfc8414#section-3.3. When authorization >> server details can be manually configured in the client, the client must >> verify that all issuer values are unique.” (Or at least something along >> those lines, I’m sure my wording can be improved. But if the client is >> correctly implementing rfc8414 or OIDC discovery [and does not have any >> manually configured authorization servers] then there’s no requirement for >> any further checks that the issuer is unique.) >> >> Joseph >> >> >> On 3 Nov 2020, at 07:01, Vladimir Dzhuvinov <vladi...@connect2id.com> >> wrote: >> >> This can potentially occur. If JARM is used "iss" becomes redundant. To >> me JARM is an "enhanced" iss. >> >> If both are included a sensible client should make sure the iss and the >> JARM iss match. >> >> My suggestion is to not require iss when a JARM is present, but in case >> both do occur to have the client check both. >> >> Vladimir >> On 02/11/2020 22:34, Takahiko Kawasaki wrote: >> >> Hi Karsten, >> >> The specification mentions JARM. Does this specification require the iss >> response parameter even when JARM is used? That is, should an authorization >> response look like below? >> >> HTTP/1.1 302 Found >> Location: https://client.example.com/cb?response={JWT}&iss={ISSUER} >> >> Or, can the iss response parameter be omitted when JARM is used? >> >> A small feedback for the 3rd paragraph in Section 4: >> s/identifes/identifies/ >> >> Best Regards, >> Taka >> >> >> On Tue, Nov 3, 2020 at 3:13 AM Vladimir Dzhuvinov < >> vladi...@connect2id.com> wrote: >> >>> Thanks Karsten, looks good to me now, no further comments. >>> >>> Vladimir >>> On 02/11/2020 09:54, Karsten Meyer zu Selhausen wrote: >>> >>> Hi all, >>> >>> Daniel and I published a new version of the "iss" response parameter >>> draft to address the feedback from the WG. >>> >>> Changes in -01: >>> >>> - Incorporated first WG feedback >>> - Clarifications for use with OIDC >>> - Added note that clients supporting just one AS are not vulnerable >>> - Renamed metadata parameter >>> - Various editorial changes >>> >>> >>> We would like to ask you for further feedback and comments on the new >>> draft version. >>> >>> Best regards, >>> Karsten >>> >>> -------- Forwarded Message -------- >>> Subject: New Version Notification for >>> draft-meyerzuselhausen-oauth-iss-auth-resp-01.txt >>> Date: Sun, 01 Nov 2020 23:31:42 -0800 >>> From: internet-dra...@ietf.org >>> To: Karsten Meyer zu Selhausen <karsten.meyerzuselhau...@hackmanit.de> >>> <karsten.meyerzuselhau...@hackmanit.de>, Karsten zu Selhausen >>> <karsten.meyerzuselhau...@hackmanit.de> >>> <karsten.meyerzuselhau...@hackmanit.de>, Daniel Fett >>> <m...@danielfett.de> <m...@danielfett.de> >>> >>> >>> A new version of I-D, draft-meyerzuselhausen-oauth-iss-auth-resp-01.txt >>> has been successfully submitted by Karsten Meyer zu Selhausen and posted >>> to the >>> IETF repository. >>> >>> Name: draft-meyerzuselhausen-oauth-iss-auth-resp >>> Revision: 01 >>> Title: OAuth 2.0 Authorization Server Issuer Identifier in Authorization >>> Response >>> Document date: 2020-11-01 >>> Group: Individual Submission >>> Pages: 10 >>> URL: >>> https://www.ietf.org/archive/id/draft-meyerzuselhausen-oauth-iss-auth-resp-01.txt >>> Status: >>> https://datatracker.ietf.org/doc/draft-meyerzuselhausen-oauth-iss-auth-resp/ >>> Html: >>> https://www.ietf.org/archive/id/draft-meyerzuselhausen-oauth-iss-auth-resp-01.html >>> Htmlized: >>> https://tools.ietf.org/html/draft-meyerzuselhausen-oauth-iss-auth-resp-01 >>> Diff: >>> https://www.ietf.org/rfcdiff?url2=draft-meyerzuselhausen-oauth-iss-auth-resp-01 >>> >>> Abstract: >>> This document specifies a new parameter "iss" that is used to >>> explicitly include the issuer identifier of the authorization server >>> in the authorization response of an OAuth authorization flow. If >>> implemented correctly, the "iss" parameter serves as an effective >>> countermeasure to "mix-up attacks". >>> >>> >>> >>> 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. >>> >>> The IETF Secretariat >>> >>> >>> -- >>> Karsten Meyer zu Selhausen >>> IT Security Consultant >>> Phone: +49 (0)234 / 54456499 >>> Web: https://hackmanit.de | IT Security Consulting, Penetration >>> Testing, Security Training >>> >>> Does your OAuth or OpenID Connect implementation use PKCE to strengthen the >>> security? Learn more about the procetion PKCE provides and its limitations >>> in our new blog >>> post:https://www.hackmanit.de/en/blog-en/123-when-pkce-cannot-protect-your-confidential-oauth-client >>> >>> Hackmanit GmbH >>> Universitätsstraße 60 (Exzenterhaus) >>> 44789 Bochum >>> >>> Registergericht: Amtsgericht Bochum, HRB 14896 >>> Geschäftsführer: Prof. Dr. Jörg Schwenk, Prof. Dr. Juraj Somorovsky, Dr. >>> Christian Mainka, Dr. Marcus Niemietz >>> >>> >>> _______________________________________________ >>> OAuth mailing listOAuth@ietf.orghttps://www.ietf.org/mailman/listinfo/oauth >>> >>> _______________________________________________ >>> 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 >> >> >> _______________________________________________ >> 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
