[Openid-specs-fapi] Issue #295: Possible support for "embedded" SCA mode (openid/fapi)

Ralph Bragg ralph.bragg at raidiam.com
Thu Jun 4 08:18:22 UTC 2020


I agree with Dave and  strongly echo Joseph’s opinion. A CIBA flow is a better way to meet the regulatory requirement. I’d rather the AS remain in control about ultimately authenticating the user. A TPP doesn’t actual care they just want access in an easy way that doesn’t disrupt their ui/ux.

If a mechanism is really required where a tpp can say “look at me I’ve got the customers password or totp” it can be passed as part of the login_token_hint and ultimately ignored by the aspsp if it chooses too.

Signing and encrypting the login token hint would protect this in transit and ensure a way that only a valid tpp could present it and that it could be decrypted by the target aspsp.

My 2 cents

________________________________
From: Openid-specs-fapi <openid-specs-fapi-bounces at lists.openid.net> on behalf of Torsten Lodderstedt via Openid-specs-fapi <openid-specs-fapi at lists.openid.net>
Sent: Thursday, June 4, 2020 9:01:50 AM
To: Joseph Heenan <joseph at authlete.com>
Cc: Torsten Lodderstedt <torsten at lodderstedt.net>; Openid-specs-fapi <openid-specs-fapi at lists.openid.net>; dgtonge <issues-reply at bitbucket.org>
Subject: Re: [Openid-specs-fapi] Issue #295: Possible support for "embedded" SCA mode (openid/fapi)

XYZ is different in that it generally starts with the backend call and leaves the decision about next steps to the AS while the AS‘s decision is governed by the client‘s capabilities.

In case of OAuth2, the client decided the interaction pattern (based on its capabilities and (potentially) AS metadata) and uses the respective endpoint at the AS and passes flow specific parameters.

Using another endpoint and grant type better fits the OAuth2 design philosophy. Please note: there are already other backend endpoint based flows in place, e.g. the device flow. Using CIBA to piggyback another flows seem a bit arbitrary to me.

Moreover, CIBA is still OIDC not OAuth. If we gone base this work on CIBA, I suggest to make it OAuth.

Am 04.06.2020 um 09:53 schrieb Joseph Heenan <joseph at authlete.com>:

I think I agree with Dave, if I’ve correctly understood his position. Some of the concepts seem similar, in particular a back channel endpoint for initiating an authorization and auth_req_id as a handle for that request and that is accepted at the token endpoint.

Expanding the existing endpoint would in some ways look similar to how an authorization is initiated in oauth.xyz<http://oauth.xyz>.

I think the main advantage I would see to reusing parts of CIBA / extending CIBA would be that the RP/AS is in a position to be flexible. Whilst the PSD2 proponents for embedded probably don’t care about it, it gives the option for the AS to decide to run a CIBA flow /or/ an embedded flow taking advantage of extra information it has about the user about which flow is available / more likely to succeed at this point in time. I don’t think it’d be unreasonable to extend that with a response that says “nah, for this user [or in this situation where I’ve decided fraud risk is high] you’re going to have to do a redirect based flow”. It could potentially even return multiple possible methods to the RP, which could be advantageous - i.e. “here’s how you proceed with embedded flow, but actually if you’re on a mobile device and the user has an app installed that will handle <some url> then you might want to use that as there’s a 100% higher chance the flow will complete successfully”.

Joseph


On 4 Jun 2020, at 08:42, Torsten Lodderstedt via Openid-specs-fapi <openid-specs-fapi at lists.openid.net<mailto:openid-specs-fapi at lists.openid.net>> wrote:

The ultimate exchange at the token endpoint might be similar, the flow isn’t. I would rather adopt the pattern then the particular grant type.

Am 04.06.2020 um 09:40 schrieb Dave Tonge <dave.tonge at momentumft.co.uk<mailto:dave.tonge at momentumft.co.uk>>:


I agree that a new endpoint is probably best. However I'd still like to explore the flow as an extension of CIBA, the reason being:
 - no new grant type needed
 - method of getting tokens already established
 - it is closer to the CIBA flow than the standard redirect flow

On Thu, 4 Jun 2020 at 09:32, Torsten Lodderstedt via Openid-specs-fapi <openid-specs-fapi at lists.openid.net<mailto:openid-specs-fapi at lists.openid.net>> wrote:
Embedded SCA is a multi step authentication/authorization process with a variety of different methods. I think, if we gone support it, we should define a new endpoint for it. Otherwise, CIBA endpoints are cluttered with additional logic specific to embedded.

> Am 03.06.2020 um 16:23 schrieb dgtonge via Openid-specs-fapi <openid-specs-fapi at lists.openid.net<mailto:openid-specs-fapi at lists.openid.net>>:
>
> New issue 295: Possible support for "embedded" SCA mode
> https://bitbucket.org/openid/fapi/issues/295/possible-support-for-embedded-sca-mode
>
> Dave Tonge:
>
> There is currently a legislative requirement for some banks in the EU to allow TPPs to use an “embedded' mode where the TPP collects the user’s credentials and passes them through to the bank.
>
> While this is not our recommended approach, maybe we should consider a way of supporting it. This would help with harmonisation efforts so that we can try and get FAPI adopted more widely.
>
> This is how the Berlin Group support this type of interaction:
>
> ![](https://bitbucket.org/repo/K7gLBb/images/3573164385-Screenshot%202020-06-03%20at%2016.11.01.png)
> It is important to note that there is a requirement for the TPP to receive back a challenge to present to a user.
>
> One idea for how to implement this would be to use CIBA as it already has the concept of an “authorization session” via the auth\_req\_id.
>
> The flow could be:
>
> * RP → AS: /bc-authorize Create authorization request with a parameter indicating that embedded auth is preferred
> * AS → RP: Ask the user for username/password
> * RP → AS /token \{auth\_req\_id, auth\_params: \{user, password\}\}
> * AS → RP: Ask the user for OTP
> * RP → AS /token \{auth\_req\_id, auth\_params: \{OTP\}\}
> * AS → RP Token
>
> No new endpoints would be needed. We would need extensions to the backchannel authentication endpoint and the token endpoint.
>
>
>
>
>>
>>
>>
> Responsible: Dave Tonge
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