[Openid-specs-fapi] JWT Secured Authorization Response Mode (#155)

Brian Campbell bcampbell at pingidentity.com
Mon Aug 20 20:59:25 UTC 2018


Thanks, Torsten, for all your work and the quick updates on this. I've got
the few more comments (from a not necessarily comprehensive review) below
but the comments are getting more and more nitpicky rather than
substantial, which to me means it's getting close to being ready.

[RFC6750] & [RFC7636], are used "2. Terms and definitions" but aren't in
the "1. Normative references"

When FAPI is expanded anywhere it should now be Financial-grade API, no?

I think it might be worthwhile to have a §4.1.3 that more generally speaks
to other response types (like the various combinations from OIDM). It
wouldn't have to cover them all specifically but maybe just say something
to the effect of all authorization endpoint response parameters are
conveyved as claims/parameters of the JWT. The way it is now with §4.1.1
for code and §4.1.2 for token kinda sorta suggest that those two are all
that's supported. I realize other parts of the document say otherwise but I
can see it being a point of confusion.

I wonder if the "jwt" shortcut mode is worthwhile to have or if it's better
to have the client simply be explicit about it using? I'm not sure I have a
strong opinion about it but just wanted to raise the question. If it's
kept, the defaults should probably also speak to the other response types
from OIDM (default for code alone is query and everything else is
fragment).
http://openid.net/specs/oauth-v2-multiple-response-types-1_0.html#Combinations
spells it out and maybe a reference with context of the jwt.fragment where
fragment is used in OIDM and jwt.qurery where qurey is used in OIDM would
work.

Probably it should also say somewhere that jwt.query encoding must not be
used for response types that contain "token" or "id_token" so as to avoid
leakage etc from having those things in the URL. Unless the JWT response is
encrypted, in which case it would be okay.

In 4.4: Maybe change "The key might be a private key registered with the
expected issuer of the response "to  "The key might be a private key, where
the corresponding public key is registered with the expected issuer of the
response" or something like that just to be clear about what part of the
key is used for what.

Also in 4.4 change "determine" to "determined" and "neede" to "needed"

Given that 4.4 is calling out checks on iss and aud, it should maybe also
say to check the exp. That's already implied by JWT in general but seems
maybe worth calling out in the processing rules along with the other
checks.

In "5. Client Metadata" and/or somewhere else in the doc, should the JWS
"none" alg be prohibited?

In §5 and §6 JWS [RFC7515] is used but 7515 isn't in the references.













On Mon, Aug 20, 2018 at 1:59 AM Torsten Lodderstedt via Openid-specs-fapi <
openid-specs-fapi at lists.openid.net> wrote:

> Hi Filip,
>
> good point! I added text on extension parameters.
>
> I also added an IANA Consideration section (registration of new client
> registration and server metadata parameters) and text on publication of
> supported response mode values.
>
>
> https://bitbucket.org/openid/fapi/src/155-JWT-Secured-Authorization-Response-Mode/Financial_API_JWT_Secured_Authorization_Response_Mode.md
>
> kind regards,
> Torsten.
>
> > Am 19.08.2018 um 19:27 schrieb Filip Skokan <panva.ip at gmail.com>:
> >
> > Hello Torsten,
> >
> > Some specs, e.g. session management define additional authorization
> endpoint response parameters (session_state in case of session management).
> > It’d be great to define if these additional params belong in the jwt or
> are sent using the regular response mode.
> >
> > Best,
> > Filip
> >
> > Odesláno z iPhonu
> >
> > 19. 8. 2018 v 17:47, Torsten Lodderstedt via Openid-specs-fapi <
> openid-specs-fapi at lists.openid.net>:
> >
> >> Hi all,
> >>
> >> I incorporated Brian’s and Vladimir’s comments/proposals.
> >>
> >> Here is a list of the changes:
> >> - moved state into the JWT
> >> - adopted processing rules to logic as defined below
> >> - added response mode values to be able to distinguish query, fragment
> and form post encoding
> >> - added form post encoding
> >> - added client and server metadata
> >>
> >> Take a look:
> https://bitbucket.org/openid/fapi/src/155-JWT-Secured-Authorization-Response-Mode/Financial_API_JWT_Secured_Authorization_Response_Mode.md
> >>
> >> Looking forward for your feedback.
> >>
> >> kind regards,
> >> Torsten.
> >>
> >>> Am 17.08.2018 um 19:24 schrieb Brian Campbell <
> bcampbell at pingidentity.com>:
> >>>
> >>> Yeah, I think that captures the general processing flow.
> >>>
> >>> On Fri, Aug 17, 2018 at 8:50 AM Torsten Lodderstedt <
> torsten at lodderstedt.net> wrote:
> >>> Hi Brian,
> >>>
> >>>> Am 17.08.2018 um 15:39 schrieb Brian Campbell <
> bcampbell at pingidentity.com>:
> >>>>
> >>>> Good point. OIDC Core (
> http://openid.net/specs/openid-connect-core-1_0.html#Security) does not
> discuss this attack angle. From your perspective, what is the typical way
> to detect crafted/modified ID Tokens in the id_token flow?
> >>>>
> >>>> Checking the signature. But if the issuer isn't known or expected,
> don't go trying to find keys for it, just reject the token.
> >>>
> >>>
> >>> I would like to summarize the discussion regarding handling of state
> value and response processing.
> >>>
> >>> From what I understand, the processing would work as follows (assuming
> the „state" is carried in the JWT):
> >>>
> >>> 1) decrypt JWT using the client's private key - the key is determine
> by the „kid“ header parameter
> >>> 2) obtain „state“ from JWT
> >>> 3) check binding of state value to user agent, if check fails - abort
> processing
> >>> 4) obtain „iss" from JWT
> >>> 5) check whether „iss" is known and expected („aud“ could be checked
> in this step as well), if not abort processing
> >>> 6) obtain signing key based on „iss“ and „kid"
> >>> 7) check signature, if signature validation fails - abort processing
> >>> 8) use response parameters
> >>>
> >>> Does this capture your thoughts correctly?
> >>>
> >>> Kind regards,
> >>> Torsten.
> >>>
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