[Openid-specs-mobile-profile] Review comments on openid-client-initiated-backchannel-authentication-core-01

Brian Campbell bcampbell at pingidentity.com
Tue Feb 5 17:41:26 UTC 2019

A few additional little comments inline:

On Mon, Feb 4, 2019 at 11:56 PM Dave Tonge <dave.tonge at momentumft.co.uk>

> On Sun, 3 Feb 2019 at 17:01, Torsten Lodderstedt <torsten at lodderstedt.net>
> wrote:
> — The second paragraph describes the way to ensure the RP is entitled to
>> obtain PPIDs for a certain sector identifier. I see two drawbacks:
>> 1) only the host component of the URIs involved is used to check for
>> equality. This means RP’s residing on the same host in a shared environment
>> automatically share the same sector identifier even if they are good
>> citizens and use different sector identifier URIs. This is basically an
>> issue of the OpenID Connect Core spec.
> Yep, I see this issue - but we should probably raise it against OIDC Core

I believe it has been raised
but would be a breaking change to finalized spec(s) so isn't likely to

>> — The third paragraph specifies in rather weak language how the client
>> shall demonstrate possession of the respective private keys. Moreover, the
>> check is deferred to the actual use of the CIBA functions. In contrast, in
>> case of standard OIDC the check whether a redirect_uri belongs to the
>> authorized destinations for certain PPIDs is checked at registration time.
>> Deferring the check to the CIBA use puts the respective RP record in kind
>> of a middle state.
>> Have you considered to let the dynamic registration function of the OP
>> perform the check? One could use one of the methods cited in the spec (mTLS
>> or private_key_jwt) to conduct the proof. Such an approach would allow to
>> conduct all the checks necessary in one place and a single action and
>> either accept or refuse the registration.
> I agree that it would be preferable for the check to be performed at
> registration time. I'm not sure if this requires a normative change -
> possibly some additional guidance would help. I've opened this issue:
> https://bitbucket.org/openid/mobile/issues/152/guidance-around-verification-of-ownership
In many cases clients aren't actually dynamically registered but configured
with the AS/OP via some other means. Also I suspect that defining/using
client authentication methods for registration is nowhere near as
straightforward as it might seem.

- section 7.1.
>> — client_notification_token - limiting the size of the token to 1024
>> characters seems a bit short in case the RP decides to use self contained
>> tokens (e.g. JWTs).
> I thought that we discussed this, but I'm struggling to find the issue. @Joseph
> Heenan <joseph.heenan at fintechlabs.io> or @Brian Campbell
> <bcampbell at pingidentity.com> can you remember?

This is the one

I chose 1024 somewhat arbitrarily to "allow for a reasonable sized JWT to
be used as the client_notification_token" but I suppose it depends on what
one views as "reasonable". I think 1024 is enough though.

>> — user_code - I think I understand the rationale of this feature but I’m
>> a bit concerned about its practicability. It shall ensure no CIBA request
>> is sent out to the user’s authentication device without prior confirmation
>> using a secret the user knows. It reminds me of the static PIN codes in the
>> Mastercard 3DS authorization scheme. It failed simply because users set up
>> and immediately forgot their PIN codes resulting in terrible conversion
>> rates. I bet user’s will most likely forget this use code as well. 3DS
>> solved the problem by introducing dynamic PIN codes, e.g. sent to the user
>> via text message. That’s most likely not a viable solution for CIBA (:—)).
>> This is a valid concern, but perhaps the difference here is that users
> won't be forced to use the mechanism. The idea is that they will have to
> explicitly opt-in to get this added protection. @Petteri Stenius
> <Petteri.Stenius at ubisecure.com> do you have any thing else to add here?
> Perhaps we need some guidance around this issue?
The whole mechanism is optional FWIW.

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