Re: [GNAP] Support of FIDO

*	Having said that, the Client could optionally use FIDO to authenticate the User and somehow transmit that to the AS.

Agree, this can be done now, we are also looking at some delegation mechanisms in WebAuthn to accomplish this 

From: TXAuth <txauth-bounces@ietf.org> On Behalf Of Dick Hardt
Sent: Thursday, August 13, 2020 11:21 AM
To: Denis <denis.ietf@free.fr>
Cc: txauth@ietf.org
Subject: Re: [GNAP] Support of FIDO

OAuth 2.0 goal was not to get rid of usernames and passwords. It was to stop site A from asking for the user's username and password at site B so that site A could access resources at site B.

How the AS authenticates the User is out of scope, and I think should be out of scope. There are a plethora of authentication mechanisms, and standardizing how the user authenticates is not required for interop. Sharing the "quality" of the authentication is an area of standardization that has been done in OpenID Connect, and I think should be included in GNAP.

Having said that, the Client could optionally use FIDO to authenticate the User and somehow transmit that to the AS.

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On Thu, Aug 13, 2020 at 10:31 AM Denis <denis.ietf@free.fr <mailto:denis.ietf@free.fr> > wrote:

This topic has already been tackled on the list, but I open a new thread for it.

In OAuth 2.0, one of the goals was to get rid of IDs and passwords. Since the solution in OAuth 2.0 was to use access tokens, 
there have been used everywhere, even when they were not strictly needed. 

It is also possible to get rid of IDs and passwords using FIDO. FIDO discloses no private information at all about the user 
and no trust relationships need to be defined since there is no AS. 

FIDO should be one allowed possibility for the user authentication. In the case of FIDO, the user is authenticated under a pseudonym 
specific to the RS. It may observed that there is no equivalent in OAuth because of the two different semantics of the subject claim.

RFC 7519 states:

The "sub" (subject) claim identifies the principal that is the subject of the JWT.  The claims in a JWT are normally statements about the subject.  
The subject value MUST either be scoped to be locally unique in the context of the issuer or be globally unique.

In one case, it is possible to link the subject claim of two users between two RSs (i.e. using a locally unique identifier in the context of the issuer) 
while in the other case (i.e. using a globally unique identifier) it is possible, in addition, to link the subject claim between one RS and any other server 
(i.e. not supporting OAuth) that is using the same globally unique identifier.

None of these two semantics fit with the FIDO use case where the subject value is scoped to be locally unique in the context of one RS. 
Hence, the linkage of users between two RSs (or between one RS and any other server) becomes impossible.  

There are cases where a user would like to enjoy the unlinkeability properties of FIDO which cannot be met using the claims currently defined in OAuth.

Denis

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