Brian,
Eric said: "what is the RP supposed to do when they encounter it? This
seems kind of under specified".
After reading your explanations below, it looks like the RP can do
anything he wants with the "actor".
It is a "claimed actor" and, if we keep the concept, it should be called
as such. Such a claim cannot be verified.
A RP could copy and paste that claim in an audit log. No standard action
related to the content of such a claim
can be specified in the spec. If the content of a "claimed actor" is
used by the RP, it should be only used as an hint
and thus be subject to other verifications which are not specified in
this specification.
Denis
Eric, I realize you weren't particularly impressed by my prior
statements about the actor claim but, for lack of knowing what else to
say, I'm going to kind of repeat what I said about it over in the
Phabricator tool
<https://mozphab-ietf.devsvcdev.mozaws.net/D4278#inline-1600> and add
a little color.
The actor claim is intended as a way to express that delegation has
happened and identify the entities involved. Access control or other
decisions based on it are at the discretion of the consumer of the
token based on whatever policy might be in place.
There are JWT claims that have concise processing rules with respect
to whether or not the JWT can be accepted as valid. Some examples are
"aud" (Audience), "exp" (Expiration Time), and "nbf" (Not Before) from
RFC 7519. E.g. if the token is expired or was intended for someone or
something else, reject it.
And there are JWT claims that appropriately don't specify such
processing rules and are solely statements of fact or circumstance.
Also from RFC 7519, the "sub" (Subject) and "iat" (Issued At) claims
are good examples of such. There might be application or policy
specific rules applied to the content of those kinds of claims (e.g.
only subjects from a particular organization are able to access tenant
specific data or, less realistic but still possible, disallow access
for tokens issued outside of regular business hours) but that's all
outside the scope of a specification's definition of the claim.
The actor claim falls into the latter category. It's a way for the
issuer of the token to tell the consumer of the token what is going
on. But any action to take (or not) based on that information is at
the discretion of the token consumer. I honestly don't know it could
be anything more. And don't think it should be.
There are two main expected uses of the actor claim (that I'm aware of
anyway) that describing here might help. Maybe. One is a human to
human delegation case like a customer service rep doing something on
behalf of an end user. The subject would be that user and the actor
would be the customer service rep. And there wouldn't be any chaining
or nesting of the actor. The other case is so called service chaining
where a system might exchange a token it receives for a new token that
it can use to call a downstream service. And that service in turn
might do another exchange to get a new token suitable to call yet
another downstream service. And again and so on and turtles all the
way. I'm not necessarily endorsing that level of granularity in
chaining but it's bound to happen somewhere/sometime. The nested actor
claim is able to express that all that has happened with the top level
or outermost one being the system currently using the token and prior
systems being nested.. What actually gets done with that information
is up to the respective systems involved. There might be policy about
what system is allowed to call what other system that is enforced. Or
maybe the info is just written to an audit log somewhere. Or something
else. I don't know. But whatever it is application/deployment/policy
dependent and not specifiable by a spec.
On Fri, Apr 13, 2018 at 6:38 PM, Eric Rescorla <e...@rtfm.com
<mailto:e...@rtfm.com>> wrote:
Hi folks,
I've gone over draft-ietf-oauth-token-exchange-12 and things seem
generally OK. I do still have one remaining concern, which is about
the actor claim. Specifically, what is the RP supposed to do when they
encounter it? This seems kind of underspecified.
In particular:
1. What facts am I supposed to know here? Merely that everyone in
the chain signed off on the next person in the chain acting as
them?
2. Am I just supposed to pretend that the person presenting the token
is the identity at the top of the chain? Say I have the
delegation A -> B -> C, and there is some resource which
B can access but A and C cannot, should I give access?
I think the first question definitely needs an answer. The second
question I guess we could make not answer, but it's pretty hard
to know how to make a system with this left open..
-Ekr
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