Re: [OAUTH-WG] Followup on draft-ietf-oauth-token-exchange-12.txt

[Brian Campbell <[e-mail]>]

I suspect that the vast majority of time C's permissions won't matter at
all. But I do think there are legitimate cases where they might be
considered in the policy decision. One general example I can think of is a
customer service rep or administrator taking override type corrective
action on an end-user's account or transaction information (A is the
end-user and C is the customer service rep) that the user on their own
wouldn't have permission to change.

On Fri, Jun 1, 2018 at 3:47 PM, Eric Rescorla <[e-mail]> wrote:

> That would go a long way, I think. Do you think that C's permissions
> matter at all? So, say that the resource is accessible to C but not A?
>
> -Ekr
>
>
>
>
> On Fri, Jun 1, 2018 at 11:47 AM, Brian Campbell <
> [e-mail]> wrote:
>
>> Hi Eric,
>>
>> Apologies for my somewhat slow response. I've honestly been unsure of how
>> else to try and address the comment/question. But will continue trying...
>>
>> My expectation would be that access control decisions would be made based
>> on the subject of the token itself or on the current actor. And maybe a
>> combination of both in some situations (like, for example, the actor is an
>> administrator and the token allows admin level access to the stuff the
>> token subject would normally have access to).  However, I don't believe
>> that nested prior actors would or should be considered in access control
>> decisions. The nesting is more just to express what has happened for
>> auditing or tracking or the like. To be honest, the nesting was added in
>> the draft largely because the structure naturally and easily allowed for it
>> and it seemed like it might be useful information to convey in some cases.
>>
>> So in that A->B->C case (the claims of such a token would, I think, look
>> like the JSON below), B *is not* giving C his authority. B is just noted
>> in the token as having been involved previously.  While A is identified as
>> the subject of the token and C is the current actor.
>>
>>     {
>>       "aud":"... ,"iss":... , "exp":..., etc. etc. ...
>>       "sub":"A",
>>       "act":
>>       {
>>         "sub":"C",
>>         "act":
>>         {
>>           "sub":"B"
>>         }
>>       }
>>     }
>>
>>
>> Would some text explicitly saying that only the token subject (top level
>> sub and claims) and the party identified by the outermost "act" claim (the
>> current actor) are to be considered in access control decisions address
>> your concern?
>>
>>
>> On Tue, May 29, 2018 at 4:19 PM, Eric Rescorla <[e-mail]> wrote:
>>
>>> Hi Brian,
>>>
>>> To be clear, I'm not opposing Delegation. My concern here is that we
>>> have a chain of signed assertions and I'm trying to understand how I as a
>>> consumer of those assertions am supposed to evaluate it.
>>>
>>> I don't think it's sufficient to just say that that the access control
>>> rules are local policy, because then the entity generating the signature
>>> has no way of knowing how its signature will be used.
>>>
>>> To go back to the case I gave in my initial e-mail, say we have a chain
>>> A->B->C and a resource that A and C could ordinarily not access, but B can.
>>> If C has this delegation, can C access the resource? I.e., is B giving C
>>> his authority or just passing on A's authority? It seems pretty important
>>> for B to know that before he gives the token to C.
>>>
>>> -Ekr
>>>
>>>
>>> On Thu, May 17, 2018 at 11:06 AM, Brian Campbell <
>>> [e-mail]> wrote:
>>>
>>>> Delegation has been in the document since its inception and throughout
>>>> the three and a half years as a working group document.
>>>>
>>>> From a process point of view, the document is now in AD Evaluation. I
>>>> worked through a number of questions and clarifications with Eric (said
>>>> AD), however he raised the particular questions that started this thread on
>>>> the WG list. And I responded with an attempt at addressing those questions.
>>>> That was about a month ago.
>>>>
>>>> Eric, was my explanation helpful in clarify anything for you? Is there
>>>> some text that you'd like to see added? Something else? I'm unsure how to
>>>> proceed but would like to move things forward.
>>>>
>>>>
>>>> On Thu, May 17, 2018 at 8:03 AM, Bill Burke <[e-mail]> wrote:
>>>>
>>>>> This is an honest question: How important is the actor stuff to the
>>>>> players involved?  Are people going to use it?  IMO, its an edge case
>>>>> and I think more important areas, like external token exchange (realm
>>>>> to realm, domain to domain) are being neglected.  I'm quite unfamiliar
>>>>> how consensus is reached in this WG or the IETF, so I hope I'm not
>>>>> sounding rude.  Just trying to provide some constructive feedback.
>>>>>
>>>>>
>>>>>
>>>>> On Thu, May 17, 2018 at 9:26 AM, Mike Jones <
>>>>> [e-mail]> wrote:
>>>>> > Moving the actor claim to a separate specification would only make
>>>>> things more complicated for developers.  There already plenty of OAuth
>>>>> specs.  Needlessly adding another one will only make related things harder
>>>>> to find.
>>>>> >
>>>>> > Just like in the JWT [RFC 7519] spec itself in which use of all the
>>>>> claims is optional, use of the actor claim in this spec.  If you don't need
>>>>> it, don't use it.  Just because some won't use it is no better an argument
>>>>> for moving it to a different spec than the argument that JWT should have
>>>>> defined each of its claims in different specs.  That would have made things
>>>>> harder, not easier.
>>>>> >
>>>>> >                                 -- Mike
>>>>> >
>>>>> > -----Original Message-----
>>>>> > From: OAuth <[e-mail]> On Behalf Of Bill Burke
>>>>> > Sent: Thursday, May 17, 2018 2:11 PM
>>>>> > To: Brian Campbell <[e-mail]>
>>>>> > Cc: oauth <[e-mail]>
>>>>> > Subject: Re: [OAUTH-WG] Followup on draft-ietf-oauth-token-exchang
>>>>> e-12.txt
>>>>> >
>>>>> > My personal opinion is that I'm glad this actor stuff is optional.
>>>>> > For one, none of our users have asked for it and really only do
>>>>> simple exchanges.  Secondly, the rules for who can exchange what for what
>>>>> is controlled and defined within our AS.  Makes things a lot simpler on the
>>>>> client.  I kind of wish the actor stuff would be defined in a separate
>>>>> specification.  I don't see us implementing it unless users start asking us
>>>>> to.
>>>>> >
>>>>> > On Wed, May 16, 2018 at 6:11 PM, Brian Campbell <
>>>>> [e-mail]> wrote:
>>>>> >> Well, it's already called the "actor claim" so the claimed part is
>>>>> >> kind of implied. And "claimed actor claim" is a rather awkward.
>>>>> >> Really, all JWT claims are "claimed something" but they don't
>>>>> include
>>>>> >> the "claimed" bit in the name. RFC 7519, for example, defines the
>>>>> >> subject claim but not the claimed subject claim.
>>>>> >>
>>>>> >> On Fri, Apr 20, 2018 at 11:38 AM, Denis <[e-mail]> wrote:
>>>>> >>>
>>>>> >>> 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 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-mail]>
>>>>> 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
>>>>> >>>>
>>>>> >>>>
>>>>> >>>> _______________________________________________
>>>>> >>>> OAuth mailing list
>>>>> >>>> [e-mail]
>>>>> >>>> https://www.ietf.org/mailman/listinfo/oauth
>>>>> >>>>
>>>>> >>>
>>>>> >>>
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>>>>> >>> _______________________________________________
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>>>>> >>>
>>>>> >>>
>>>>> >>> _______________________________________________
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>>>>> >>>
>>>>> >>
>>>>> >>
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>>>>> >>
>>>>> >
>>>>> >
>>>>> >
>>>>> > --
>>>>> > Bill Burke
>>>>> > Red Hat
>>>>> >
>>>>> > _______________________________________________
>>>>> > OAuth mailing list
>>>>> > [e-mail]
>>>>> > https://www.ietf.org/mailman/listinfo/oauth
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Bill Burke
>>>>> Red Hat
>>>>>
>>>>
>>>>
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>>>
>>>
>>>
>>
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>
>

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