Re: [GNAP] Should access tokens be opaque or not for the clients ?

Adrian Gropper <agropper@healthurl.com> Fri, 19 March 2021 01:04 UTC

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From: Adrian Gropper <agropper@healthurl.com>
Date: Thu, 18 Mar 2021 21:03:51 -0400
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To: Alejandro Iacobelli <aiacobelli.sec@gmail.com>
Cc: Fabien Imbault <fabien.imbault@gmail.com>, txauth gnap <txauth@ietf.org>, Justin Richer <jricher@mit.edu>, Steve Moore <srmoore@gmail.com>
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Subject: Re: [GNAP] Should access tokens be opaque or not for the clients ?
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I'm not a security person. I do, however, have a lot of experience with
regulatory practices as relates to safety in medical devices and business.
I see the security struggles of today as being an over-reliance on
institutional trust and a lack of effective audit and individual
accountability. I see great promise in moving advanced crypto to the
individual through DIDs and VCs and then using these identity-based
components in protocols like GNAP that are directly in the security, audit,
and accountability role. DIDs, VCs, and capabilities, to me, are just data
models.

I know that's a very vague and philosophical answer to give to architects
like the folks in this group. Sorry.

>From this perspective, GNAP is where we get to introduce
individual accountability, resilience against single points of failure,
practical audit mechanisms, and the benefit of a decade of
blockchain-driven cryptography advances. I don't see GNAP as complicated,
but what do I know?

Adrian

On Thu, Mar 18, 2021 at 8:24 PM Alejandro Iacobelli <
aiacobelli.sec@gmail.com> wrote:

> The decision about "opaque" vs "sealed but recoverable" or "signed"
> access_token goes way back on the stateless protocols session management.
>
> In my opinion, the software design principle that we must apply here is
> the "need to know" principle. This means, the less information an attacker
> could get, the better. One thing that JWS explse is all the context
> information about a token, so an attacker can get lots of information just
> with a look.
>
> The next discussion will be what ways of generating opaque tokens are
> there and which must we choose (Encrypted vs CSPRNG based).
>
> On Thu, 18 Mar 2021 at 21:17, Fabien Imbault <fabien.imbault@gmail.com>
> wrote:
>
>> Hi Adrian,
>>
>> I'm really not sure I understand here.
>>
>> I get the idea of putting a policy engine in front of your services to
>> implement ZTA. But I'm not sure I get this way of framing things. It blurs
>> functional roles and actual services, and most importantly if everything
>> gets its own AS, it also gets by transitivity its RO'/RQ' (and then its
>> AS-RO' etc) and so the complexity becomes staggering.
>> Why do we need that?
>>
>> Fabien
>>
>> Le ven. 19 mars 2021 à 00:55, Adrian Gropper <agropper@healthurl.com> a
>> écrit :
>>
>>> +1 This aligns with my healthcare use-case to the extent that Justin can
>>> transfer the capability granted by that QR code to Adrian who happens to be
>>> nearby Steve's house.
>>>
>>> I've tried to capture some of this in my comment to #145
>>> https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/145#issuecomment-802388458
>>>
>>> - Adrian
>>>
>>> On Thu, Mar 18, 2021 at 2:39 PM Justin Richer <jricher@mit.edu> wrote:
>>>
>>>> Right, and in the GNAP model this becomes something my client instance
>>>> presents to the AS when I show up. The AS can validate my presentation of
>>>> this item and give my client instance a token to call Steve’s RS. Or if you
>>>> wanted to get super fancy Steve’s AS could even challenge my client
>>>> instance and get a cryptographic response to prove I have the thing Steve
>>>> had me scan. But in both cases it’s part of things that the AS collects in
>>>> order to create the access token.
>>>>
>>>>  — Justin
>>>>
>>>> On Mar 18, 2021, at 2:26 PM, Stephen Moore <srmoore@gmail.com> wrote:
>>>>
>>>> That in my mind works out great... Say I'm logged into my home hub/AS.
>>>> Justin is over and agrees to cat sit, I pull up my client app, and generate
>>>> a QR code that has maybe The AS URI, the HomeHub API URL, and the 'special
>>>> token to present to AS for a real token'. Justin scans that QR code with
>>>> his home controller app, and BAM, he's onboarded as a guest without even
>>>> logging into my AS or me dealing with his Auth provider.
>>>> -steve
>>>>
>>>> On Thu, Mar 18, 2021 at 2:08 PM Justin Richer <jricher@mit.edu> wrote:
>>>>
>>>>> I think Steve’s use case gives an interesting example of something
>>>>> that I believe Adrian’s been talking about as well — delegating to another
>>>>> person.
>>>>>
>>>>> We traditionally think of delegation at the AS to mean “a different
>>>>> user account logs in to the AS”, and it’s important to know that this does
>>>>> in fact work. But this could just as easily be “Steve sends his friend an
>>>>> artifact to present to the AS to get access”. This isn’t Steve (or Steve’s
>>>>> client software) getting and sending an access token, this is sending some
>>>>> other set of rights credential to his friend, or his friend’s software. So
>>>>> then Steve’s AS can have policy that says “when I see this rights
>>>>> credential, give an access token for the following attenuated things,
>>>>> because Steve said so”. The AS doesn’t even ever need to know who Steve’s
>>>>> friend is!
>>>>>
>>>>> And importantly here, we don’t expect Steve’s friend to bring their
>>>>> own AS to the party. Steve’s RS has no reason to trust his friend’s AS, let
>>>>> alone his friend’s client. But Steve’s AS is in a position to know more
>>>>> about the rights policies that Steve wants to apply, and so it can use
>>>>> other technologies like VC’s, DIDs, OIDC, or any number of other things to
>>>>> let things go through. This pattern is exactly why I think we need to think
>>>>> of this in terms of what’s currently called “interaction” at the AS. It’s
>>>>> not really just about how the end-user interacts, it’s about how the AS
>>>>> gathers all the consent and authorization information. I plan to rewrite
>>>>> section 4 to that effect.
>>>>>
>>>>>  — Justin
>>>>>
>>>>> On Mar 18, 2021, at 1:58 PM, Stephen Moore <srmoore@gmail.com> wrote:
>>>>>
>>>>> I'm having some concerns with the way you're flipping the trust here
>>>>> Denis. You seem to indicate that the user has trust in the RS and the
>>>>> Client and has to gain the trust of the AS. I feel like the least
>>>>> trustworthy portion of the architecture is the client, because that seems
>>>>> like it is the most interchangeable component.
>>>>>  Let me explain by way of a use case I have in mind.
>>>>> Let's say I have a smart home. I have devices and data storage and
>>>>> rule engines that are parts of sensors and hubs I buy for the house. I have
>>>>> a trust in those devices, because it's hardware, if the company is leaking
>>>>> data at the hardware level there isn't much I can do other than buy
>>>>> different sensors.
>>>>> In this case, the primary home hub, which is under control of the
>>>>> homeowner, would also be the AS, as well as a policy agent.  Authentication
>>>>> in the example is outsourced to whatever auth providers you want. I set up
>>>>> my home using a google account, a friend is staying and wants access and
>>>>> uses FB for auth... whatever.
>>>>> The part that I have little control over is the client my friend uses
>>>>> on his phone. Or if I change the client on the tablet in the kitchen to try
>>>>> out something new. These pieces might be single page web apps, they might
>>>>> be downloaded apps, etc. I do not want them having any additional
>>>>> information than is necessary. If I give my friend permission to unlock the
>>>>> door, and control the lights because they are feeding my cats while I'm
>>>>> away, the client doesn't need to know anything beyond, I see this home
>>>>> controller, and I have access to these lights and that door lock.
>>>>>
>>>>> In your scenarios, the client is spy by design, and if it is a web
>>>>> app, I don't trust them to not grab my user email address from the AS and
>>>>> put it on a mailing list it sells to some sketchy company, when the only
>>>>> other component that needs that information is the RS.
>>>>>
>>>>> -steve
>>>>>
>>>>> On Thu, Mar 18, 2021 at 1:21 PM Denis <denis.ietf@free.fr> wrote:
>>>>>
>>>>>> I have changed the title of this thread, since the original topic has
>>>>>> been closed.
>>>>>>
>>>>>> Justin, you are raising the following question:
>>>>>>
>>>>>> The question I have is — why does the client need to know what’s in
>>>>>> the token?
>>>>>> Not if they could possibly know, but why would we expect a client to
>>>>>> know and manage the contents of the token?
>>>>>>
>>>>>> The answer is quite simple: so that the end-user may have confidence
>>>>>> into the architecture.
>>>>>> The seventh of the eleven privacy principles from ISO 29100 (page 14)
>>>>>> is:
>>>>>>
>>>>>> *7. Openness, transparency and notice *
>>>>>>
>>>>>> If the access token is considered as a black box for the end-user, it
>>>>>> cannot be confident about the content of the access token.
>>>>>> Such access token may disclose some private information without the
>>>>>> consent of the end-user. If the access token that it has obtained
>>>>>> does not match with what has been requested, the client will first
>>>>>> not forward the access token to the RS and then will complain about the AS.
>>>>>>
>>>>>> Denis
>>>>>>
>>>>>>
>>>>>> Hi Justin,
>>>>>>
>>>>>> "The access token is fundamentally a conversational artifact between
>>>>>> the AS and the RS which the client is the carrier of."
>>>>>> That's right, and a good opportunity to distinguish between the need
>>>>>> for token inspection (i.e. a runtime verification, wherever that may be)
>>>>>> and the need to negotiate the token format (a discovery). That last
>>>>>> part could very well be an extension, as a way to open up the ecosystem
>>>>>> beyond JWTs (which are fine, but come with their own limitations).
>>>>>>
>>>>>> Fabien
>>>>>>
>>>>>> On Thu, Mar 18, 2021 at 5:59 PM Justin Richer <jricher@mit.edu>
>>>>>> wrote:
>>>>>>
>>>>>>> On Mar 18, 2021, at 11:30 AM, Alan Karp <alanhkarp@gmail.com> wrote:
>>>>>>>
>>>>>>>
>>>>>>> Justin Richer <jricher@mit.edu> wrote:
>>>>>>>
>>>>>>>> On Mar 18, 2021, at 12:08 AM, Alan Karp <alanhkarp@gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> Adrian Gropper <agropper@healthurl.com> wrote:
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Is there an AS involved in the delegation? How and where in the
>>>>>>>>> lifecycle of the protected resource?
>>>>>>>>>
>>>>>>>>
>>>>>>>> If tokens are certificates, the AS need not be involved in
>>>>>>>> subsequent delegations.  The AS must be involved if the tokens are opaque.
>>>>>>>>
>>>>>>>>
>>>>>>>> Tokens are opaque to the client instance. They are not opaque to
>>>>>>>> the AS. They might be opaque to the RS, but that depends on the kind of
>>>>>>>> relationship the RS and AS have. GNAP should allow different options here
>>>>>>>> as there are different use cases for that.
>>>>>>>>
>>>>>>>
>>>>>>> Tokens are not opaque to the client in SPKI, zcap-ld, Orie's
>>>>>>> implementation with VCs, or our Zebra Copy work.  Why must they be in GNAP?
>>>>>>>
>>>>>>>
>>>>>>> The existence of the AS is exactly the reason for this. The AS is
>>>>>>> the role that “knowledge about the token contents” has been outsourced to
>>>>>>> in the GNAP model (which is based on the OAuth model).
>>>>>>>
>>>>>>> It brings significant simplicity for the client developer. The
>>>>>>> question I have is — why does the client need to know what’s in the token?
>>>>>>> Not if they could possibly know, but why would we expect a client to know
>>>>>>> and manage the contents of the token?
>>>>>>>
>>>>>>> The access token is fundamentally a conversational artifact between
>>>>>>> the AS and the RS which the client is the carrier of. The client is not the
>>>>>>> audience of the token, nor the creator of the token, nor even the manager
>>>>>>> of the token and the rights it represents. The client as a simple carrier
>>>>>>> is a powerful model that allows the security layer to get out of the way of
>>>>>>> the actual application logic that developers want to do.
>>>>>>>
>>>>>>>  — Justin
>>>>>>>
>>>>>>>
>>>>>>> --------------
>>>>>>> Alan Karp
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Mar 18, 2021 at 4:56 AM Justin Richer <jricher@mit.edu>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> On Mar 18, 2021, at 12:08 AM, Alan Karp <alanhkarp@gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> Adrian Gropper <agropper@healthurl.com> wrote:
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Is there an AS involved in the delegation? How and where in the
>>>>>>>>> lifecycle of the protected resource?
>>>>>>>>>
>>>>>>>>
>>>>>>>> If tokens are certificates, the AS need not be involved in
>>>>>>>> subsequent delegations.  The AS must be involved if the tokens are opaque.
>>>>>>>>
>>>>>>>>
>>>>>>>> Tokens are opaque to the client instance. They are not opaque to
>>>>>>>> the AS. They might be opaque to the RS, but that depends on the kind of
>>>>>>>> relationship the RS and AS have. GNAP should allow different options here
>>>>>>>> as there are different use cases for that.
>>>>>>>>
>>>>>>>> It would probably be worthwhile to separate the portions of the
>>>>>>>> spec that talk about the RS-AS relationship into its own standalone
>>>>>>>> document. A similar approach was taken in UMA2 and it was helpful. (Though
>>>>>>>> admittedly, as with anything, there are missteps there that we can
>>>>>>>> hopefully learn from.)
>>>>>>>>
>>>>>>>>  — Justin
>>>>>>>>
>>>>>>>>
>>>>>>>> --------------
>>>>>>>> Alan Karp
>>>>>>>>
>>>>>>>>
>>>>>>>> On Wed, Mar 17, 2021 at 8:54 PM Adrian Gropper <
>>>>>>>> agropper@healthurl.com> wrote:
>>>>>>>>
>>>>>>>>> Sure!
>>>>>>>>>
>>>>>>>>> Is there an AS involved in the delegation? How and where in the
>>>>>>>>> lifecycle of the protected resource?
>>>>>>>>>
>>>>>>>>> Also your use of "the client" seems to imply that either there is
>>>>>>>>> only one client or the client doesn't matter. Which is it?
>>>>>>>>>
>>>>>>>>> Adrian
>>>>>>>>>
>>>>>>>>> On Wed, Mar 17, 2021 at 11:43 PM Fabien Imbault <
>>>>>>>>> fabien.imbault@gmail.com> wrote:
>>>>>>>>>
>>>>>>>>>> Thanks for that.
>>>>>>>>>>
>>>>>>>>>> Trying to reframe it:
>>>>>>>>>> GNAP is defined as a delegation protocol so the main intent is
>>>>>>>>>> related to a delegate of the RO (i.e. the end user) that wishes to access
>>>>>>>>>> the RO's protected resources, through the client.
>>>>>>>>>>
>>>>>>>>>> Fabien
>>>>>>>>>>
>>>>>>>>>> Le jeu. 18 mars 2021 à 04:29, Adrian Gropper <
>>>>>>>>>> agropper@healthurl.com> a écrit :
>>>>>>>>>>
>>>>>>>>>>> At various points in the lifecycle of the protected resource the
>>>>>>>>>>> client at the resource server (RS) might be:
>>>>>>>>>>>
>>>>>>>>>>>    - The RO (subject) user agent trading payment for a service
>>>>>>>>>>>    promise
>>>>>>>>>>>    - The RO user agent using the promise to access the
>>>>>>>>>>>    protected resource
>>>>>>>>>>>    - A delegate of the RO user agent using a different client
>>>>>>>>>>>
>>>>>>>>>>> What's vague is where the GNAP AS enters the picture as
>>>>>>>>>>> described above. How would you describe it?
>>>>>>>>>>>
>>>>>>>>>>> Adrian
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Wed, Mar 17, 2021 at 10:20 PM Fabien Imbault <
>>>>>>>>>>> fabien.imbault@gmail.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Hi Adrian
>>>>>>>>>>>>
>>>>>>>>>>>> I'm still confused why you're saying the terminology is vague.
>>>>>>>>>>>> I get the "power" neutrality is not to your liking, but RQ /
>>>>>>>>>>>> user agent is no better in my view.
>>>>>>>>>>>>
>>>>>>>>>>>> Can you elaborate?
>>>>>>>>>>>>
>>>>>>>>>>>> Fabien
>>>>>>>>>>>>
>>>>>>>>>>>> Le jeu. 18 mars 2021 à 00:18, Adrian Gropper <
>>>>>>>>>>>> agropper@healthurl.com> a écrit :
>>>>>>>>>>>>
>>>>>>>>>>>>> I'm sure you're right. Our vague terminology around
>>>>>>>>>>>>> client and end-user leads to my confusion. If GNAP is primarily about
>>>>>>>>>>>>> delegation then, of course, we should avoid any incentives to impersonate
>>>>>>>>>>>>> or we're wasting our time. This is partly why I'm trying to study up on
>>>>>>>>>>>>> capabilities and asking for expert advice from folks like Alan Karp and
>>>>>>>>>>>>> Mark Miller (cc'd)
>>>>>>>>>>>>>
>>>>>>>>>>>>> As best I can understand it, the RS has only two choices, it
>>>>>>>>>>>>> can:
>>>>>>>>>>>>>
>>>>>>>>>>>>>    - store an attribute of the RO a [DID, email address, GNAP
>>>>>>>>>>>>>    AS URL], or
>>>>>>>>>>>>>    - hand the RO a capability as a sort-of promise and avoid
>>>>>>>>>>>>>    making any entries in an ACL or equivalent.
>>>>>>>>>>>>>
>>>>>>>>>>>>> When a token comes back to the RS, it will either be:
>>>>>>>>>>>>>
>>>>>>>>>>>>>    - validated according to something associated with the
>>>>>>>>>>>>>    stored RO attribute, or
>>>>>>>>>>>>>    - signed by the RS itself.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Either way, trust in the client seems moot.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Adrian
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Wed, Mar 17, 2021 at 5:29 PM Justin Richer <jricher@mit.edu>
>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Mar 17, 2021, at 4:55 PM, Adrian Gropper <
>>>>>>>>>>>>>> agropper@healthurl.com> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Wed, Mar 17, 2021 at 4:23 PM Tobias Looker <
>>>>>>>>>>>>>> tobias.looker@mattr.global> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> <snip>
>>>>>>>>>>>>>>> > A client might not have a DID but it could have a VC as a
>>>>>>>>>>>>>>> certificate of authenticity linked to some audit mechanism.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> To me a VC would come under the assertions umbrella (that is
>>>>>>>>>>>>>>> to say a VC could be one type of valid assertion). The client may possess
>>>>>>>>>>>>>>> or been presented with a VC that it could include in its request to the AS
>>>>>>>>>>>>>>> as a way to identify the subject and perhaps prove authentication and
>>>>>>>>>>>>>>> authorization.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I do not assume that the client that interacts with the AS to
>>>>>>>>>>>>>> make a request and receive a token is the same as the client that will
>>>>>>>>>>>>>> present the token to the RS. In the US HIPAA use-case, for example, the
>>>>>>>>>>>>>> root of trust is a contract between the patient-subject and the
>>>>>>>>>>>>>> doctor-requesting party but the doctor workflow is expected to delegate the
>>>>>>>>>>>>>> token to some other end-user that may be using a totally different client
>>>>>>>>>>>>>> such as an EHR.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> If the client that gets the token is not same as the client
>>>>>>>>>>>>>> that uses the token, that is a violation of core security principles as it
>>>>>>>>>>>>>> allows for (and really designs for) impersonation by client software. I
>>>>>>>>>>>>>> would have no reason to trust client software that would hand its
>>>>>>>>>>>>>> credentials over to another piece of software, and in fact I shouldn’t
>>>>>>>>>>>>>> trust it.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I think you may be conflating several different kinds of
>>>>>>>>>>>>>> parties under the “client” umbrella here, though. It’s entirely possible
>>>>>>>>>>>>>> that one client might call an RS that in turn acts as a client for
>>>>>>>>>>>>>> something else down stream. But each of those hops is different from the
>>>>>>>>>>>>>> last.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>  — Justin
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>> --
>>>>>> TXAuth mailing list
>>>>>> TXAuth@ietf.org
>>>>>> https://www.ietf.org/mailman/listinfo/txauth
>>>>>>
>>>>> --
>>>>> TXAuth mailing list
>>>>> TXAuth@ietf.org
>>>>> https://www.ietf.org/mailman/listinfo/txauth
>>>>>
>>>>>
>>>>>
>>>> --
>>>> TXAuth mailing list
>>>> TXAuth@ietf.org
>>>> https://www.ietf.org/mailman/listinfo/txauth
>>>>
>>> --
>>> TXAuth mailing list
>>> TXAuth@ietf.org
>>> https://www.ietf.org/mailman/listinfo/txauth
>>>
>> --
>> TXAuth mailing list
>> TXAuth@ietf.org
>> https://www.ietf.org/mailman/listinfo/txauth
>>
>
>
> --
> You know nothing Jon Snow!
> --
> TXAuth mailing list
> TXAuth@ietf.org
> https://www.ietf.org/mailman/listinfo/txauth
>