UMA learns how to simplify, simplify

It seems like a good time to review where we’ve been and where we’re going in the process of building User-Managed Access (UMA).

The introduction to our draft protocol spec reads:

The User-Managed Access (UMA) 1.0 core protocol provides a method for users to control access to their protected resources, residing on any number of host sites, through an authorization manager that makes access decisions based on user policy.

For example, a web user (authorizing user) can authorize a web app (requester) to gain one-time or ongoing access to a resource containing his home address stored at a “personal data store” service (host), by telling the host to act on access decisions made by his authorization decision-making service (authorization manager). The requesting party might be an e-commerce company whose site is acting on behalf of the user himself to assist him in arranging for shipping a purchased item, or it might be his friend who is using an online address book service to collect addresses, or it might be a survey company that uses an online service to compile population demographics.

While this introduction hasn’t changed much over time, the UMA protocol itself has undergone a number of changes, some of them dramatic. The changes came from switching “substrates”, partly in response to the recent volatility that has entered the OAuth world with the introduction of WRAP and partly in an ongoing effort to make everything simpler.

Here’s an attempt to convey the once and future UMA-substrate picture:

uma-history

Back in the days of ProtectServe, we did try to use “real OAuth” to associate various UMA entities, but in one area we “cheated” (that is, used something OAuth-ish but not conforming) to get protocol efficiencies and to ensure the privacy of the authorizing user. Hence the wavy line.

Once the UMA effort started in earnest at Kantara, we discovered a way to use three instances of “real OAuth” instead, and decided to (as we thought of it) “get out of the authentication business” entirely — thus theoretically allowing people to build UMA implementations on top of OAuth as a fairly thin shim. However, the trick we had discovered to accomplish this, along with (it must be admitted) an over-enthusiasm for website metadata discovery loops, made the spec pretty dense and hard to understand and we weren’t satisfied with that either.

As of last week, we have moved to a WRAP substrate on an interim basis, and that approach is what’s in our spec now. Although WRAP’s entities sound an awful lot like UMA’s entities (authorization manager/authorization server, host/protected resource, requester/client, authorizing user/resource owner), it took us a while to disentangle the different use cases and motivations that drove the development of each set, and in retrospect I’m glad we don’t have the same exact language. It allows us to have a meaningful conversation about the ways in which WRAP can gracefully assume a “plumbing” role for UMA (and other) use cases, and the ways in which we need to extend and profile it.

Here’s a diagram that summarizes the current state of the UMA protocol and the role(s) WRAP plays in it (click to enlarge):

UMA protocol summary

Given our use cases, it pretty much flows naturally, and it solves the problems we were previously tying ourselves in knots over. (Do check out the details if you have that sort of inquiring mind. Though reading our spec now benefits from an existing understanding of the WRAP paradigm — we plan to add more detail to make it stand better on its own — it’s now a lot more to-the-point.)

So all in all, I’m very pleased about our direction, and about the increasing interest we’re seeing from all over the place. But we’re not there yet, and it’s partly because over at the IETF they’re still working on OAuth Version 2.0, and that’s what we’re really after. We have been active in contributing use cases and feedback to the OAuth WG, and I think next week’s meeting at IETF 77 will be productive for all.


Come to the Kantara UMA workshop at the beginning of the European Identity Conference on May 4! (fixed; used to say May 3)


Though UMA isn’t fully incubated yet, it also seems like a good time to give a shout-out to all the UMAnitarians (join us… don’t be afraid…) who are helping with the process, with special thanks to our leadership team: Paul Bryan, Domenico Catalano, Maciej Machulak, Hasan ibne Akram, and Tom Holodnik.

Tags: , , , ,

Comments are closed.