[Openid-specs-fapi] a look at CIBA

Brian Campbell bcampbell at pingidentity.com
Tue Jun 19 20:53:04 UTC 2018

Thanks Dave. I do plan to join the call tomorrow so will talk to you (all)

On Tue, Jun 19, 2018 at 1:26 PM, Dave Tonge <dave.tonge at momentumft.co.uk>

> Thanks Brian, this is really useful.
> There are definitely some editorial issues with the current CIBA drafts
> that need addressing.
> We're going to discuss Sarah's proposal on the call tomorrow. As FAPI we
> want to have a spec (or specs) that support so called "decoupled" flows.
> When we looked around CIBA was the closest to this kind of flow that we
> could find.
> If you can make the call tomorrow it would be great so we can discuss
> further.
> Thanks
> Dave
> On Tue, 19 Jun 2018 at 20:54, Brian Campbell via Openid-specs-fapi <
> openid-specs-fapi at lists.openid.net> wrote:
>> On a recent-ish Wednesday bi-weekly FAPI call I was *encouraged* to
>> review the CIBA stuff. This email is the result of my attempting to do
>> that. I say attempting because I found the task rather difficult and time
>> consuming to do. So this 'review' isn't comprehensive (or necessarily
>> coherent or organized). I tried to touch on what seem like important
>> things. And a few trivial bits snuck in too.
>> It's somewhat difficult to know what to review as
>> Financial_API_WD_CIBA.md references what seems to be the most recent
>> published CIBA draft, which is dated March 6, 2017. The xml source file in
>> the MODRNA Mercurial repo, however, has seen a number of commits in the
>> year+ since that time.
>> It's rather unconventional and awkward for FAPI to try and profile or use
>> a draft spec from a different WG in a different vertical. It might work
>> okay if CIBA was a generally applicable and a stable standard but it's
>> still very much just a draft and has some MODRNA specifics in it.
>> Isn't this really more of an out-of-band authorization than it is
>> 'backchannel' user authentication? The CIBA name and even use of id tokens
>> and user authentication don't quite click for me.
>> I'm no stranger to typos myself so can't be too critical here but the
>> MODRNA CIBA draft has an unusually large number of typos (misspellings,
>> missing words, that kind of thing). Most are simple editorial issues but it
>> leaves the impression that the document hasn't gotten much attention or is
>> neglected or even abandoned. I gave up trying write down all the editorial
>> issues but there is one (that I saw anyway) typo that's more than just
>> editorial n a parameter name where sec 7.3 defines "expires in”,
>> which, based on convention and the parameter name in the example below, I
>> assume should be "expires_in".
>> The format of the Authentication Request isn’t defined sufficiently. The
>> example shows a POST with application/json in the body while the text
>> defers to authorization/authentication request of OAuth/OIDC, which uses
>> application/x-www-form-urlencoded parameters. I see the idea behind CIBA
>> wanting to just kinda reuse the OAuth 2.0 Authorization Request in this
>> back-channel context but I think it actually causes more issues than it
>> solves. And it'd be more appropriate and straightforward for CIBA to
>> directly define the parameters and format/encoding.
>> CIBA says the OP "MUST validate the hint provided (login_hint,
>> login_token_hint or id_token_hint). e.g.: If a signature is provided it
>> MUST be checked. If a validity date is provided it MUST be checked." For
>> id_token_hint in particular this is really problematic as an ID Token is
>> issued for a different context to a different audience and typically with a
>> shortish validity period. OIDC core kind of touches on the issue by saying
>> the AS need not be listed as an audience of the ID Token when used as an
>> id_token_hint value. The id_token_hint from OIDC core isn't the most
>> clearly defined parameter to begin with and while CIBA defers to OIDC for
>> it's definition the usage is somewhat different. But potentially more
>> important to a CIBA flow. As it is, consistent and interoperable treatment
>> of id_token_hint seems unlikely.
>> CIBA has a new endpoint sometimes called Backchannel Authentication
>> Endpoint and sometimes called bc-authorize (also kinda implying that should
>> be the actual path, which shouldn't be dictated by spec).  A new endpoint
>> should be introduced/described and define (and register) a new
>> Authorization Server Metadata parameter for it that allows the AS to
>> determine the endpoint URI and provide it in metadata. The device flow does
>> this with its Device Authorization Endpoint
>> https://tools.ietf.org/html/draft-ietf-oauth-device-flow-09#section-7.3
>> which is similar in many respects to CIBA's new endpoint and is a good
>> pattern to follow. There are other missing IANA registrations too.
>> CIBA says to authenticate to the Backchannel Authentication Endpoint
>> using the authentication method registered for its client_id. But then goes
>> on to say that the RECOMMENDED authentication method is with an Signed
>> Request Object. But there is no OAuth client authentication method
>> corresponding to Signed Request Object. There's no signed request authn to
>> the token endpoint. The client authn stuff needs to be rationalized.
>> In one or two places CIBA says that errors from the new endpoint "MUST
>> return an error response, per Section of [OpenID.Core].” which is
>> nonsensical because that's a redirect to the client's redirect uri. A
>> different section of CIBA does define 40x error response codes for the new
>> endpoint, which is more appropriate. But it contradicts it's own MUST.
>> Having acr_values be a required parameter of the "Authentication Request"
>> might work for MODRNA (I don't know) but I don't think makes sense in a
>> more general cases.
>> The treatment of refresh tokens seems a bit inconsistent with some text
>> sounding like an RT will/must always be returned. Other text is more clear
>> that it's optional, as is the case with other OAuth flows/grants, and how
>> it should also be throughout CIBA.
>> Extension grant types are full URIs by definition from RFC6749 but CIBA
>> intermixes backchannel_request and urn:openid:params:modrna:
>> grant‑type:backchannel_request.
>> This email seems entirely too long yet incomplete. And I'm not sure how
>> to end it. But that's all for now.
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> --
> Dave Tonge
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