[Openid-specs-ab] acr values

Anthony Nadalin tonynad at microsoft.com
Mon Aug 12 20:49:39 UTC 2013

In some cases the RP may not understand all what the IdP is saying, like state of the session, the RP may not deal or care with session state, may only deal with authentication strength and relies on short lived tokens for enforcing sessions, so what would you expect the RP to do with the combined URI in your example?

From: Tim Bray [mailto:tbray at textuality.com]
Sent: Monday, August 12, 2013 1:46 PM
To: Anthony Nadalin
Cc: <openid-specs-ab at lists.openid.net>
Subject: Re: [Openid-specs-ab] acr values

An RP.

On Mon, Aug 12, 2013 at 1:30 PM, Anthony Nadalin <tonynad at microsoft.com<mailto:tonynad at microsoft.com>> wrote:
Who do you want to say something about the “session strength” to?

From: openid-specs-ab-bounces at lists.openid.net<mailto:openid-specs-ab-bounces at lists.openid.net> [mailto:openid-specs-ab-bounces at lists.openid.net<mailto:openid-specs-ab-bounces at lists.openid.net>] On Behalf Of Tim Bray
Sent: Monday, August 12, 2013 1:05 PM
To: <openid-specs-ab at lists.openid.net<mailto:openid-specs-ab at lists.openid.net>>
Subject: [Openid-specs-ab] acr values

In our IDP role, we’re coming under a lot of pressure to say something about “session strength” and maybe in some circumstances force re-auth and so on.  There are a lot of different vocabularies in play that you could use to talk about this stuff, including NIST and ISO publications; and the work of the Fido alliance is maybe interesting.  So I expect a lot of churn in this space, and OIDC needs to allow sufficient elbow room.
So, the purpose of this note is to confirm my understandings, based on looking at the OIDC Messages draft.  Do people agree with these?
- It’s perfectly OK to provide any old URI we dream up as a value for the “acr” claim.
- There may be awkwardness around multiple values; suppose I wanted to assert, for example, that the session is less than ten minutes old AND two-factor authent was used.    All I can think of is composing a URI along the lines of urn:google-auth-claims?max-age=10&two-factor=true; which is a little kludgy but I guess OK.  Awkward, though, in the case where there’s a Fido vocabulary for 2-factor-flavor and someone else’s vocabulary for session-freshness.

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