Re: [GNAP] Will GNAP support Zero Trust Architecture?

Adrian Gropper <> Thu, 25 March 2021 02:41 UTC

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From: Adrian Gropper <>
Date: Wed, 24 Mar 2021 22:41:02 -0400
Message-ID: <>
To: Fabien Imbault <>
Cc: Alan Karp <>, Mark Miller <>, Benjamin Kaduk <>, Justin Richer <>, GNAP Mailing List <>
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Subject: Re: [GNAP] Will GNAP support Zero Trust Architecture?
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Thank you for creating the issue. My definition of AS is independent of
I also agree with Alan's definition based on delegation. An AS-RS would be
a delegate of the RS.

Based on that, I see it as obvious that the policy has to be accessible
(defined locally?) in order for it to be run as the code that turns a
request into an access token.

The only other possibility is that the request is packaged by the AS and
sent elsewhere (an agent) for evaluation against policy and a proto-token
returned. In that case the AS is acting as a proxy and the PDP is
elsewhere. I can imagine that an AS-RS would behave this way so that the
proto-token could be turned into an access token by the AS-RS. Isn't this
what Justin is proposing? In this design, the AS is the AS-RS and the agent
is the AS-RO. By my definition, this model has two ASs since both are
processing requests into tokens. The problem with this is complexity and
privacy. The RO may not want to share the request information with the


On Wed, Mar 24, 2021 at 5:21 PM Fabien Imbault <>

> Isn't that what the AS is supposed to be, only with the caveat that the
> policy is defined locally?
> Fabien
> Le mer. 24 mars 2021 à 20:17, Alan Karp <> a écrit :
>> AS-RO is an AS that RO trusts to delegate RO's access tokens according to
>> RO's policies.
>> --------------
>> Alan Karp
>> On Wed, Mar 24, 2021 at 9:36 AM Fabien Imbault <>
>> wrote:
>>> Hi Alan and Adrian,
>>> I've created issue AS-RO policy delegation (
>>> to
>>> capture your input.
>>> A first question that arises: can we give a definition to AS-RO?
>>> Thanks
>>> Fabien
>>> On Tue, Mar 23, 2021 at 4:15 PM Alan Karp <> wrote:
>>>> Fabien Imbault <> wrote:
>>>>> Hi Alan,
>>>>> Yes, but in that flow, the token relationship between AS-RS and AS-RO
>>>>> is only secure if the tokens issued by AS-RS are cryptographically
>>>>> attenuable in the first place.
>>>> Attenuated delegation is a requirement, but that doesn't have to be
>>>> done cryptographically.  Token exchange works just fine.  SPKI and zcap-ld
>>>> are examples of the crypto approach, and we used token exchange in the
>>>> system for HP.
>>>> --------------
>>>> Alan Karp
>>>> On Tue, Mar 23, 2021 at 4:12 AM Fabien Imbault <
>>>>> wrote:
>>>>> Hi Alan,
>>>>> Yes, but in that flow, the token relationship between AS-RS and AS-RO
>>>>> is only secure if the tokens issued by AS-RS are cryptographically
>>>>> attenuable in the first place.
>>>>> Fabien
>>>>> On Mon, Mar 22, 2021 at 9:26 PM Alan Karp <> wrote:
>>>>>> Justin Richer <> wrote:
>>>>>>> But with all that in mind, I think the key here is going to be
>>>>>>> looking at what the inputs to the AS are, and how those can be defined in
>>>>>>> an interoperable way for AS’s that can accept them. I think there’s a lot
>>>>>>> of room for innovation and flexibility here that doesn’t break the trust
>>>>>>> model or core use cases. If I have an AS-RS set that won’t accept my
>>>>>>> favorite flavor of policy engine inputs, then I can decide not to use that
>>>>>>> one. But this is a very different question than saying the RS itself needs
>>>>>>> to accept my own AS — and we can’t keep conflating these two models.
>>>>>>> I agree.  The point of having an AS-RO is to allow RO to specify a
>>>>>> policy for which of RO's access tokens should be delegated under what
>>>>>> conditions.  AS-RS should not need to understand those policies.  The flow
>>>>>> would be
>>>>>>    - RO contacts AS-RS and gets one or more access tokens.
>>>>>>    - RO delegates one or more of those tokens, potentially
>>>>>>    sub-scoped, to AS-RO.
>>>>>>    - A different user contacts AS-RO to get a potentially sub-scoped
>>>>>>    access token from AS-RO.
>>>>>>    - That user presents the access token delegated by AS-RO when
>>>>>>    invoking the resource.
>>>>>> AS-RS only needs to verify that the delegation chain is legitimate,
>>>>>> e.g., no increase in scope, and that it grants permission for the request
>>>>>> being made.  AS-RS does not need to understand the policy behind granting
>>>>>> the delegation by AS-RO.
>>>>>> --------------
>>>>>> Alan Karp
>>>>>> On Mon, Mar 22, 2021 at 11:40 AM Justin Richer <>
>>>>>> wrote:
>>>>>>> Adrian,
>>>>>>> I think this shows the problem with the terminology as it’s been
>>>>>>> applied in this conversation, which I’ve tried to shine light on before.
>>>>>>> What you and others are calling the “RS” is really the “AS and RS working
>>>>>>> together” — everything to the right of the line. When Denis had brought up
>>>>>>> “eliminating the AS” in another thread, what he’d really done is labeled
>>>>>>> everything to the right of the line as the “RS”. Of course, the irony here
>>>>>>> is that everything to the right of the line used all be called the “AS” or
>>>>>>> simply “server” in the OAuth 1 days. As you say below, I don’t want the
>>>>>>> client to have visibility on what happens on that side.
>>>>>>> Note well: The Google+ logo labeled “IdP” in the diagram is not the
>>>>>>> AS, as far as GNAP is concerned. It does not issue an access token that the
>>>>>>> RS will accept. The elements to the left of the line could be a lot of
>>>>>>> things, but they are NOT the AS — by definition. The client lives over on
>>>>>>> the left, but so do any external inputs to the AS. These could be policy
>>>>>>> inputs on behalf of the RO, they could be presentation artifacts, they
>>>>>>> could be federated logins, they could be the output of policy decisions.
>>>>>>> How the AS comes to trust those things is up to the AS’s implementation.
>>>>>>> It’s something we can talk about, but ultimately GNAP won’t be in any
>>>>>>> position to dictate because in practice some AS’s are simply going to
>>>>>>> internalize all policies and we will never successfully force those open.
>>>>>>> But with all that in mind, I think the key here is going to be
>>>>>>> looking at what the inputs to the AS are, and how those can be defined in
>>>>>>> an interoperable way for AS’s that can accept them. I think there’s a lot
>>>>>>> of room for innovation and flexibility here that doesn’t break the trust
>>>>>>> model or core use cases. If I have an AS-RS set that won’t accept my
>>>>>>> favorite flavor of policy engine inputs, then I can decide not to use that
>>>>>>> one. But this is a very different question than saying the RS itself needs
>>>>>>> to accept my own AS — and we can’t keep conflating these two models.
>>>>>>> So to me, GNAP can support a Zero Trust Architecture by LEVERAGING
>>>>>>> the AS, not by subsuming or eliminating it. It is in fact the AS, not the
>>>>>>> client and not the RS, that will request and consume the results of a
>>>>>>> privacy-preserving zero-trust policy query thing. Anything that happens
>>>>>>> downstream from that is of little concern to the zero-trust components
>>>>>>> because, as you point out, it’s on the “other side” of the line.
>>>>>>> I think we got this basic component model pretty right in OAuth: the
>>>>>>> AS and RS and client working together. Where OAuth misses the mark is the
>>>>>>> assumption that the user has to log in to the AS through a webpage and
>>>>>>> interact directly, thereby proving they’re the RO. It’s this latter space
>>>>>>> where I think we can both push innovation and also address the important
>>>>>>> and compelling use cases like the ones you’re bringing.
>>>>>>>  — Justin
>>>>>>> On Mar 22, 2021, at 2:14 PM, Adrian Gropper <>
>>>>>>> wrote:
>>>>>>> I'm sorry, Justin. As a Resource Owner, I look at the RS trust
>>>>>>> boundary (the dotted line in the diagram) as being the RS. I don't expect
>>>>>>> any visibility into what's going on on the right.
>>>>>>> My problem with the framing you propose is that requests are going
>>>>>>> to the RS (or the AS-RS) and I don't want to share my policies with the
>>>>>>> AS-RS. I want to keep the RS and AS-RS as ignorant as possible.
>>>>>>> Adrian
>>>>>>> On Mon, Mar 22, 2021 at 1:48 PM Justin Richer <>
>>>>>>> wrote:
>>>>>>>> Adrian,
>>>>>>>> What you’re discussing below, in terms of logging in to a site, is
>>>>>>>> not approaching the RS. You are in fact approaching the client, and
>>>>>>>> identifying both the AS and RS to the client. The client is a client *of
>>>>>>>> your identity* in this model, and the RS is part of the identity
>>>>>>>> provider. It’s really important that we don’t conflate the RS and client in
>>>>>>>> this way as it leads to a lot of confusion downstream and a lot of broken
>>>>>>>> trust boundaries.
>>>>>>>> With that model in mind, approaching the “RS" and providing it your
>>>>>>>> identity is really just a case of the “federated login to AS” pattern that
>>>>>>>> we discussed on the WG call. The user here approaches an RS, which has its
>>>>>>>> own AS. To share things from this RS, the RO has to authenticate to the
>>>>>>>> RS’s AS. This particular AS allows the RO to do so using an external
>>>>>>>> identity — in which case, the AS is now a “client” of a separate,
>>>>>>>> disconnected (but layered) delegation. The ultimate client that eventually
>>>>>>>> calls the RS down the way may or may not know about these layers.
>>>>>>>> <PastedGraphic-1.png>
>>>>>>>> This same AS, which is closely tied to the RS and trusted by the
>>>>>>>> RS, might also take in FIDO credentials, or DIDs, or any number of other
>>>>>>>> proof mechanisms. The output of this is an access token the RS trusts, but
>>>>>>>> the input is up to the AS. The RS is not what you’re logging in to.
>>>>>>>>  — Justin
>>>>>>>> On Mar 22, 2021, at 1:28 PM, Adrian Gropper <>
>>>>>>>> wrote:
>>>>>>>> I too am in favor of avoiding consolidation and correlation. Right
>>>>>>>> now, when I approach a service provider (RS) for the first time, I'm
>>>>>>>> offered the opportunity to identify my persona as: email, sign-in with
>>>>>>>> Google, Facebook, or Apple. I know there are people who try to create
>>>>>>>> one-off email addresses but that is mostly a waste of time.
>>>>>>>> So, along come FIDO2 and DID wallets to the rescue. Now, in theory,
>>>>>>>> I have a way to start out my RS relationship pseudonymously.
>>>>>>>> When I want my resource to be discovered or shared I will post that
>>>>>>>> RS URL including my pseudonym. If I then want to introduce a mediator in
>>>>>>>> front of my AS or messaging service endpoint, I have that option. If I want
>>>>>>>> to keep requests away from the mediator, I would publish an encryption key
>>>>>>>> along with my pseudonym.
>>>>>>>> - Adrian
>>>>>>>> On Mon, Mar 22, 2021 at 9:55 AM Justin Richer <>
>>>>>>>> wrote:
>>>>>>>>> On Mar 21, 2021, at 1:18 PM, Benjamin Kaduk <> wrote:
>>>>>>>>> >
>>>>>>>>> > On Sat, Mar 20, 2021 at 01:07:42AM -0400, Adrian Gropper wrote:
>>>>>>>>> >> @Alan Karp <> shared a talk about the
>>>>>>>>> Principle Of Least
>>>>>>>>> >> Authority (POLA) in a recent comment
>>>>>>>>> >>
>>>>>>>>> >> I recommend it.
>>>>>>>>> >>
>>>>>>>>> >> We might expect a protocol with authorization in the title to
>>>>>>>>> use authority
>>>>>>>>> >> as a core principle. I advocate for a GNAP design that
>>>>>>>>> maximizes the power
>>>>>>>>> >> of the RO, to be seen as a human rights issue when the RO is a
>>>>>>>>> human. This
>>>>>>>>> >> causes me to ask how to combine better security with better
>>>>>>>>> human rights in
>>>>>>>>> >> GNAP.
>>>>>>>>> >>
>>>>>>>>> >> Who should have the least authority in the GNAP design?
>>>>>>>>> >>
>>>>>>>>> >> The AS derives authority as a delegate of the RO. If we ask the
>>>>>>>>> RO to
>>>>>>>>> >> partition limited authority across dozens of different ASs by
>>>>>>>>> domain and
>>>>>>>>> >> function, then we are not using technology to empower the
>>>>>>>>> individual.
>>>>>>>>> >> Probably the opposite, as we introduce consent fatigue and
>>>>>>>>> burden normal
>>>>>>>>> >> people to partition their lives into non-overlapping domains.
>>>>>>>>> >>
>>>>>>>>> >> My experience says we should aim for one AS per persona because
>>>>>>>>> that maps
>>>>>>>>> >> into the way we manage our public and private identities. POLA
>>>>>>>>> would then
>>>>>>>>> >> teach care in keeping ASs and RSs related to work / public
>>>>>>>>> separate from
>>>>>>>>> >> ASs and RSs related to private life so that a policy
>>>>>>>>> vulnerability in our
>>>>>>>>> >> delegation to an AS would have the least likelihood of harm.
>>>>>>>>> >
>>>>>>>>> > Thinking about how least authority/least privilege would apply
>>>>>>>>> to GNAP
>>>>>>>>> > seems like a useful exercise.  I do want to point out some
>>>>>>>>> potential
>>>>>>>>> > pitfalls with one-AS-per-persona that we can also be aware of.
>>>>>>>>> If
>>>>>>>>> > one-AS-per-persona becomes one-persona-per-AS as well, then the
>>>>>>>>> AS's
>>>>>>>>> > identity in effect also serves as a persona identity and there
>>>>>>>>> are privacy
>>>>>>>>> > considerations to that.  If, on the other hand, the
>>>>>>>>> > multiple-personas-per-AS (presumably corresponding to multiple
>>>>>>>>> humans)
>>>>>>>>> > route is taken, we should consider whether that would lead to
>>>>>>>>> various
>>>>>>>>> > (e.g., market) forces driving consolidation to just a handful of
>>>>>>>>> > super-popular AS services.  That topic is a current matter of
>>>>>>>>> concern to
>>>>>>>>> > some IETF participants.
>>>>>>>>> >
>>>>>>>>> Hi Ben, big +1 to this. This is something that we discussed ages
>>>>>>>>> ago in the UMA working group, and it’s one of the biggest problems with the
>>>>>>>>> personal AS (and personal data store) model. This kind of thing makes
>>>>>>>>> RS-first trust models really difficult in practice.
>>>>>>>>> As a strawman, let’s say that I’ve got software that wants to
>>>>>>>>> access my medical information. It calls an RS and requests access, but it
>>>>>>>>> hasn’t been granted anything yet. Now I as the RO have set up the RS so
>>>>>>>>> that it talks to my personal AS, that only I use. In addition to the RS
>>>>>>>>> having to be able to figure out which medical records are being requested
>>>>>>>>> from the context of the unauthenticated request (which means it needs
>>>>>>>>> identifiers in the URL or something similar for the RS to be able to tell,
>>>>>>>>> assuming that it protects data for more than one person). So this client
>>>>>>>>> software doesn’t know who I am and doesn’t know my medical record
>>>>>>>>> information, makes a completely unauthorized request to the RS, and the RS
>>>>>>>>> says “Go to Justin’s personal AS to get a token”. The client can now make a
>>>>>>>>> direct correlation between the data that’s being protected at the RS and
>>>>>>>>> the person running the AS that protects it. Importantly, this client makes
>>>>>>>>> this call with no prior relationship to the RS and no really auditable way
>>>>>>>>> to track it down after the fact. This is a design feature in the good case,
>>>>>>>>> and terrifying in the bad case.
>>>>>>>>> If the RS instead says “welcome to Medicine Doctor RS, please talk
>>>>>>>>> to the Medicine Doctor AS to get access”, we haven’t exposed anything at
>>>>>>>>> all. And from the perspective of both the patient and the RS, this is more
>>>>>>>>> privacy-preserving, and it’s really the least surprising option. Once the
>>>>>>>>> client gets to the AS, it can start a negotiation of figuring out who the
>>>>>>>>> RO is for the information being accessed.
>>>>>>>>> On top of this, the usability expectations of people managing
>>>>>>>>> their own AS, or set of AS’s for multiple personas to keep things separate,
>>>>>>>>> is a huge burden. Even in the tech community, I know people who can’t
>>>>>>>>> reliably manage more than one email address for different purposes. I
>>>>>>>>> wouldn’t expect my partner to do that — they have trouble enough balancing
>>>>>>>>> all the logins and sessions required for different kids remote schooling, I
>>>>>>>>> couldn’t imagine them having to understand all the requirements for
>>>>>>>>> managing multiple authorization servers and associated policies. I also
>>>>>>>>> don’t expect any person to “manage keys” — I’ve been on the internet for
>>>>>>>>> decades and I can barely keep tabs on my GPG keys, and only use them when I
>>>>>>>>> am forced to. This is exactly the kind of “market pressure” that I think
>>>>>>>>> Ben mentions above, people will just want to outsource that to someone
>>>>>>>>> else, and the reality will be a few popular providers.
>>>>>>>>> In which case, we could end up doing a ton of work to allow an RS
>>>>>>>>> choice only to end up with a world where the RS ends up making a limited
>>>>>>>>> choice anyway. We see how that plays out with OpenID Connect — RP’s could
>>>>>>>>> allow arbitrary IdPs but they choose Google because it works and that’s
>>>>>>>>> where the users are. (And that’s not to say anything of the proprietary
>>>>>>>>> OIDC-like protocols, but that’s another discussion).
>>>>>>>>> For further reading on these topics, I recommend both “Why Johnny
>>>>>>>>> Can’t Encrypt” and “Why CSCW Systems Fail”.
>>>>>>>>> So what does this have to do with GNAP? I think we can be
>>>>>>>>> clear-eyed on what kinds of expectations we have for the participants. If
>>>>>>>>> we expect users (RO’s) to have to set up the AS-RS relationship, or expect
>>>>>>>>> them to carry their AS, or manage their personal keys — I think we’ve lost
>>>>>>>>> the battle for relevance.
>>>>>>>>>  — Justin
>>>>>>> --
>>>>>> TXAuth mailing list
>>>>> --
> TXAuth mailing list