Re: [OAUTH-WG] Question regarding RFC 8628

[Torsten Lodderstedt <[e-mail]>]

Hi Hervé,

looping in Joseph.

> On 18. Nov 2019, at 21:17, Robache Hervé <[e-mail]> wrote:
> 
> Thanks Torsten
>  
> Yes, we study this flow as well. Actually we consider the two following flows for a mobile-based authentication
>  
> -          DECOUPLED : via a RFC8628-derived or CIBA approach (as suggested by Rob)
> -          REDIRECT : via the flow specified in the OpenId link you gave.
>  
> The main issue encountered so far is to give back the focus on the third party app. Third Parties fear that their app will be kept in the back of the mobile screen.

@Joseph: what’s your take on this concern? 

> This could happen when the TPP app [app link]/[universal link] is not properly registered or forwarded to the bank app.
> -          In the REDIRECT approach this means that the authorization code cannot be forwarded to the TPP
> -          In the DECOUPLED approach it less critical since the TPP polls the bank and eventually gets its token once the PSU has authenticated.

But in the decoupled flow, the PSU first has to enter her PSU ID in order to allow the TPP to identity the PSU towards the ASPSP. This is less convenient and leaks PII.

best regards,
Torsten. 

>  
> Best regards
>  
> Hervé
>  
> De : Torsten Lodderstedt [mailto:[e-mail]] 
> Envoyé : lundi 18 novembre 2019 11:39
> À : Robache Hervé
> Cc : [e-mail]
> Objet : [OAUTH-WG] Question regarding RFC 8628
>  
> Hi Hervé,
>  
> I assume you want to allow the TPP to send the PSU to the bank’s app on the same device?
>  
> In that case, why don’t you just make the bank’s authorization endpoint URL the universal link? If the universal link is defined on the smartphone (since the bank’s app is installed), the redirect will open the app. If the app is not installed, well, it will open the authorization endpoint in the browser. A very robust and simple approach.
>  
> There is an excellent article about this topic by Joseph Hernan on openid.net https://openid.net/2019/10/21/guest-blog-implementing-app-to-app-authorisation-in-oauth2-openid-connect/.
>  
> best regards,
> Torsten.
> 
> 
> Am 18.11.2019 um 16:24 schrieb Robache Hervé <[e-mail]>:
> 
>  
> Dear all
>  
> We are considering using RFC8628 for a specific use case that is related to the version 2 of Payment Service Directive in Europe (PSD2).
>  
> The purpose of the work is to provide a decoupled authentication flow for a payment Service User (PSU) aiming to grant access to a Third Party Provider (TPP) for his/her data hosted by a Bank.
> The sequence should be as followed:
> -          Nominal flow (as specified by the RFC)
> o   The TPP asks the PSU about the Bank identity
> o   The TPP posts a Device Access Token Request to the Bank
> o   The Bank sends back a Device Access Token response to the TPP
> o   The TPP starts to poll the bank for gaining the access token
> -          Derived flow
> o   The “verification_uri_complete” will not be displayed to the PSU but used as an [app link]/[universal link] on a smartphone in order to launch the bank’s app.
> o   The bank’s app authenticates the PSU and asks for consent confirmation
> -          Back to the nominal flow
> o   The TPP gets its access token
>  
> Two questions have raised during the work
> -          As RFC8628 is supposed to work on separate devices, can the usage be extrapolated to separate apps on the same device (i.e. the PSU’s smartphone)?
> -          One issue of the derived flow is that, after authentication, the PSU is still facing the bank’s app
> o   We would like to go back to the TPP’s app as fluently as possible. The use of another [app link]/[universal link]could do the job is provided by the TPP. We consider adding this uri as an additional parameter to the “verification_uri_complete”.
> o   Is this compliant with RFC8628?
>  
> Thanks in advance for your answers.
>  
> Hervé Robache
> 
> 
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