On Thu, Feb 25, 2021, at 02:18, Justin Richer wrote:
> I agree that the NxM problem is the purview of the whole IETF, but it’s
> something that we’re particularly interested in over in GNAP. As the editor
> of OAuth’s dynamic registration extension and the GNAP core protocol, I hope
> I can add to this conversation.
>
> From a technical standpoint, OAuth’s dynamic client registration lets
> arbitrary clients talk to an AS, but the trust isn’t there in practice. On
> top of that I think this problem is exacerbated by a fundamental protocol
> design element of OAuth: the client_id that’s required. That field means
> there’s an assumption that a relationship was set up between the pieces of
> software, implied to be trusted by admins at the AS. Sure you can get that
> client_id under special circumstances, but there’s still a special weight
> handed to that and the dynamic stuff feels like you’re giving up control as
> an AS. In GNAP, the relationship is inverted, and it’s designed as
> “dynamic-first”, with pre-registered clients being an optimization on top of
> that.
Yep, this is the big point - OAuth is designed to require the the third leg of
trust that creates the NxM problem.
If that dotted line between client and server requires a pre-existing trust
relationship rather than the trust being entirely mediated by the user choosing
to connect client A with server B, then you have the NxM problem. This is the
"you can only have your John Deere tractor serviced by an approved John Deere
service centre" problem. You can only use this client with servers who have
pre-approved it. Or fall back to the "cash of the internet" - plain text
passwords.
> Does this solve the NxM problem? No, because companies are still going to
> decide that they only talk to keys or identifiers that they know ahead of
> time. But the protocol puts the dynamic case forward as baseline and fits in
> much better with the likes of JMAP than OAuth ever could:
>
> - {The Bat} creates a key pair.
> - {User} enters their email address into {Bat}, {Bat} does discovery (maybe
> that’s a JMAP thing? Webfinger?) and finds the JMAP server and the GNAP
> endpoint for authentication as an option.
> - {Bat} talks to the GNAP AS at {ISP} and presents the key it just made up.
> {ISP} has never seen this key, but knows how to talk GNAP and get the user to
> authorize {Bat} to access email.
> - {User} does this using GNAP and gets back an access token that’s tied to
> the key {Bat} made back at the beginning. That token is tied (at the {ISP})
> to the user’s account.
>
> Yes, you can do all of this today with OAuth (and people have done so), but
> OAuth’s basic model of “go do discovery and registration first and THEN talk
> to me” is a trust impediment more than it is a technical impediment. The
> “negotiation” part of the GNAP name comes from the philosophy of “start
> talking first and figure out what you need as you go”. Instead of jumping
> through hoops to get something you can trust, you just start in and then
> decide how much you trust it. A corporate rollout could use its own key
> distribution mechanism and static registration to limit which client
> instances talk back to the company server, regardless of which accounts would
> authorize access on top of that. An internet-facing service is going to be
> more likely to take a TLS approach, of “I’ll talk to you in a secure fashion
> without caring who you are right now”.
>
> We really are trying to make GNAP a consistent protocol at its core and learn
> from problems with OAuth in the wild, all while letting GNAP address a wider
> variety of use cases. I agree that GNAP could be clearer about specific use
> cases, and we’re working on the spec still so any help here is appreciated.
Excellent. This is precisely what I've been waiting for for these very many
years as a viable replacement for storing a password locally on disk. Just
having the server able to distinguish between different client instances for
the same user is a big start, because you can de-authorise one without having
to lock out every connection - even if the user is still entering their
password during the setup phase each time.
This is what Fastmail already do with our own app, creating a long-lived access
token and storing that on the device rather than storing the password itself -
and you can log out any one client from your security settings page. What's
missing is a standard way to do that with any IMAP client. The initial JMAP
authentication proposal was a very simple case of pretty much this, build into
to the protocol so everyone would do it.
Making it easy to connect up arbitrary clients with per-client tokens the
default, and easy rather than almost impossible to do in practice is where the
big difference comes in.
Bron.
--
Bron Gondwana, CEO, Fastmail Pty Ltd
[email protected]
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