W3C home > Mailing lists > Public > public-credentials@w3.org > December 2019

Re: the intersection between Swagger-style APIs and SSI/decentralized identity

From: Markus Sabadello <markus@danubetech.com>
Date: Tue, 31 Dec 2019 13:22:44 +0100
To: daniel.hardman@evernym.com
Cc: W3C Credentials CG <public-credentials@w3.org>, Justin P Richer <jricher@mit.edu>
Message-ID: <e45e513d-2b20-d273-a45f-38f24f5269b1@danubetech.com>
Hello Daniel,

Thanks for the comments, I definitely agree with all the benefits of
transport-independent messaging you describe!

Ironically, I remember a time when Sam Curren, Nathan George, and other
leaders in the Sovrin community advocated an agent architecture where
each agent "extension" would be required to publish a Swagger/OpenAPI
specification for a REST API that would be called over a DID-TLS HTTPS
connection (e.g. see slides 37-40 in this presentation
<https://docs.google.com/presentation/d/1Xw-W2hkICy6Zy86GX2t9D6zVLHHAMDMvny1YUbzaVdQ/edit#slide=id.g20d243e53b_5_6>).

Quite some time before that, in XDI messaging, we had already designed
and implemented transport-independent messages, routing, relays and
mediators, message-level security, and related concepts (e.g. see this
presentation
<https://www.oasis-open.org/committees/download.php/56309/Message%20Forwarding%20v2.pdf>).
I was very happy to see Sovrin/Indy/Aries/DIDComm then move into the
same direction and adopt the same (and even more and better!) design
patterns for transport-independent digital identity protocols.

Let me point out a few things about the proposed Work Item for Issuer
and Verifier APIs <https://github.com/w3c-ccg/community/issues/102>:

1. While I'm the one who wrote this first draft and posted the proposal,
this wasn't really my idea. It was specifically requested by the U.S.
Department of Homeland Security, to have common APIs which the different
participating startups of the Silicon Valley Innovation Program (SVIP)
should agree on. This also means that after posting the initial
proposal, I really hope I won't be the one doing most of the work on it,
especially since there are definitely other people in the community who
have more experience with credential issuing and verifying APIs than me.

2. As you note in your subsequent message in this thread, the proposed
API is only meant for INTERNAL use, for integration of an Issuer's or
Verifier's existing infrastructure with software that is able to issue
and verify credentials. This is NOT about communicating between Issuers,
Verifiers, and Holders. I'm sorry if I didn't make this clear enough. So
I think the arguments around Bolivian farmers and power imbalance don't
really apply to this. If a company or government institution wanted to
use Evernym's Verity product, or Esatus' SeLF product, or any other VC
software product built by this community, then there's usually a way how
those products can be integrated with existing enterprise
infrastructure. Such existing infrastructure may consist of legacy CRM
systems, or microservices, or Kubernetes clusters, or whatever else.
While I am sure that this integration of different internal components
could be done with DIDComm, it could also be done in other (potentially
lighter-weight) ways such as gRPC or protobuf or Webhooks or HTTP REST
APIs. The benefit of standardizing those internal interfaces is to avoid
vendor lock-in.

3. You are correct that the first draft of the proposed Issuer API
<https://app.swaggerhub.com/apis/danubetech/credential-issuer/0.0.1>
contradicts some of what I wrote above. It actually DOES have two
operations right now that don't seem to be for internal-only use; they
are even marked "Public APIs facing the Holder and Verifier" :) Those
have already been rightfully criticized by some of my SVIP colleagues,
and therefore I have added some warning text. I think those would simply
be removed as soon as the Work Item is approved, since - again -
protocols for interaction between Issuers, Verifiers, and Holders should
really be out of scope here.

4. I imagine that in a typical deployment, calling these internal Issuer
or Verifier APIs would then trigger one or more of the credential
exchange protocols that are being developed by the community, such as
the DIDComm issuance and presentation protocols, various OIDC flows,
CHAPI, etc. How exactly that would work hasn't really been discussed yet.

5. I am also definitely interested in reducing the dependency on HTTP or
Swagger. One of the objectives of this Work Item could absolutely be to
define the APIs in some abstract way, and then create the
Swagger/OpenAPI definition as merely one instance of that. I know the
Aries community is already doing some great work to bridge/convert
between DIDComm message types and Swagger/OpenAPI definitions, perhaps
we can build on this!

Markus

On 12/30/19 8:54 PM, Daniel Hardman wrote:
> Markus has recently proposed a work item for the CCG to develop
> Swagger-style APIs for issuers and verifiers. Justin has recently
> proposed a charter for a TxAuth group to start working on HTTP-based
> APIs to accomplish delegation. Digital Bazaar has advocated their
> RESTful Credential Handler API (CHAPI) in CCG and other circles as
> well. No doubt many others on this thread are aware of efforts to
> standardize APIs with similar style and similar intersection to the
> SSI/decentralized identity space.
>
> I would like to raise a red flag about such efforts, and trigger a
> thoughtful follow-up conversation. I love Swagger-style APIs and have
> advocated them extensively at past junctures of my career, but I am
> concerned that they are exactly the wrong thing to standardize right
> now. I'll explain my concerns below, in red, and then offer an
> alternative path that has most of the same benefits, in blue.
>
> 1. RESTful APIs are web-only.
>
> How do two farmers with cheap android devices in the highlands of
> Bolivia (or a Canadian Mounty and a speeder on a lonely highway in
> Yukon Territory, or friends in Frankfurt whose cell service has a
> brownlout, or two anti-government protesters) use RESTful APIs to
> transact business? If the answer is, "they subscribe to a service in
> the cloud so they can talk device-to-device," I hope we are
> embarrassed. We need something that also works over BlueTooth and
> email and other transports where a web server isn't a component.
>
> By standardizing a solution that doesn't think about these scenarios,
> we are further marginalizing them, and we are enthroning a
> /you-must-be-connected-and-you-can-be-surveilled/ model that
> guarantees /it-isnt-a-standard/ FUD for any other efforts to fix the
> problem.
>
> 2. RESTful APIs perpetuate the PKI model that we claim to be replacing
> with DIDs.
>
> Servers are authenticated in these APIs with a cert. Clients are
> authenticated with a session that follows from an OAuth token or an
> API key or basic auth material. It is possible to imagine "DID Auth"
> being used for a client of a RESTful API, and there have been several
> efforts to describe and standardize such a thing. So far, none has
> meaningful traction, so all APIs in the SSI space that use APIs are
> also allowing non-DID authentication for clients. But even if we solve
> the problem for the client side, nobody is proposing to solve the
> problem for the server side. Institutions in these APIs don't use DIDs
> for anything meaningful. Thus none of the decentralized properties of
> DIDs are brought to bear for the server side of the interaction, and
> any decentralized qualities of DIDs are relegated to minor, optional
> status for clients.
>
> 3. RESTful APIs foster a power imbalance
>
> What if there's a standard way for institutions to be a verifier or
> issuer, but no way for ordinary people to be a verifier or issuer? Or
> a standard way for institutions to delegate, but no way for ordinary
> people to do it? That's effectively what APIs like the ones I
> mentioned above guarantee. There are multiple reasons why, including:
>
>   * Institutions have web servers; farmers in Bolivia don't. (Saying
>     that they *could* is not helpful; we're just creating more
>     adoption burden for SSI by making the tech harder and more
>     expensive for them.)
>   * Servers can't make the first move in RESTful APIs; everything
>     begins when a client initiates the interaction. This makes it
>     natural for an institution (or a regulatory regime) to impose
>     terms of service or reputation criteria on a client, and unnatural
>     for a client to do the opposite. It's also convenient for hackers
>     and surveillers, since they know they can catch all interactions
>     at inception by simply listening on the server.
>   * Because these APIs are online-only, and because the server always
>     waits for the client to make the first move, they can only be
>     operated by those who have a 24x7x365 cloud presence. Institutions
>     and ordinary people don't have equal access to 24x7x365 cloud
>     capabilities.
>   * Because these APIs are secured on the server side by a cert, they
>     can only be operated by those who have access to expensive,
>     premium, centralized reputation. Again, institutions and people
>     don't have equal access to this.
>
> This is not an exhaustive list of my concerns, but I think it's enough
> to trigger a conversation.
>
> Proposed Alternative
>
> We create web APIs, but we think about them differently. We conceive
> of all of them as exchanges of messages that could also be
> accomplished over BlueTooth, email, etc. HTTP(S) is just another
> transport, where messages happen to be passed by HTTP POST (or GET, as
> appropriate). Security properties associated with the exchange are
> based on the control of DIDs and embodied in the messages themselves
> (e.g., through encryption/signing), not in a transport layer. All
> semantics for the interaction are conveyed by the message content. The
> traditional URL namespacing of Swagger can still exist, but it becomes
> less interesting, since the message content must be enough to convey
> semantics on its own (so the messages are enough in other transports).
> Either party can initiate an interaction. Institutions and people are
> actually peers.
>
> This is the world of didcomm and application-level protocols built
> atop it; it's described in Aries RFC 0003
> <https://github.com/hyperledger/aries-rfcs/blob/master/concepts/0003-protocols/README.md>.
> But before folks get their hackles up about not wanting to work with
> Aries or DIF, note that I didn't propose that Aries protocols have to
> be the basis for this approach. Instead, I proposed some
> characteristics we need to avoid. Can we explore that assertion on its
> merits, without getting immediately entangled in politics?
>
> There are already maybe 8-10 software stacks, some independent from
> top to bottom, that implement an "API" for issuing credentials and an
> "API" for verifying presentations based on the model I just
> articulated. These implementations are demonstrably interoperable with
> one another. By proposing a new work item for a Swagger API for
> issuance and verification, we are walking away from interoperability
> with these implementations, and we are incurring all of the
> architectural disadvantages I highlighted in red above.
>
> What if we did this instead?
>
>   * Agree that for issuance and verification, the goal about payloads
>     and sequencing for HTTP calls should be alignment between those
>     defined in the Aries protocol and those used by people who aren't
>     Aries-centric. This could involve give and take in either
>     direction; I'm not proposing that it has to be done by simply
>     adopting the Aries work.
>   * Agree not to depend on HTTP-specific constructs (e.g., HTTP
>     headers, HTTP status codes) to signal important semantics--so the
>     payloads could be exchanged over BlueTooth or email just as easily.
>   * Agree that, while URL namespacing gives us a nice hook into
>     Swagger-oriented tools, all semantics required for the interaction
>     are detectable from the payloads themselves.
>
> Then we'd have an HTTP solution that is Swagger-compatible but not
> limited to HTTP. The "API" we created would be interoperable on a much
> broader canvas than simple web.
>
> If we further agreed to this:
>
>   * Authentication of both parties in the interaction will be done on
>     the basis of DID control, not on the basis of certs.
>
> Then we'd also eliminate the dependence on the web's flawed PKI model,
> and the power imbalance of today's web. But I know this is more
> controversial.
>
Received on Tuesday, 31 December 2019 12:22:53 UTC

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