We've been following the fast-moving debate in the IETF regarding OAuth 2.0. OAuth, for those of you who have not encountered it already, is a set of authentication technologies for the Internet designed around the concept of an access token.
Access tokens, in the words of Eran Hammer-Lahav, are like valet keys -- they give the holder access to a specific function, for a specific amount of time. For instance, you might use OAuth to give another web site the ability to read photos from your Flickr profile, but not to modify them. OAuth lets you do this, it lets you go back to Flickr and revoke the web site's permissions at any time, and it does it without requiring that you give the site your Flickr password.
The current spec, OAuth 1.0a, is implemented in lots of places, and it solves a lot of problems. However, implementing it is no picnic for either the API provider (the server) or for the developer who builds the client. (There are libraries, of course, not to mention products such as our own that simplify this process.)
OAuth 2.0 introduces many changes. The most important is that a client may now use a "bearer token." That's a fancy IETF way of saying that an access token can just be a string that the server gives you. On every request, the client passes that token back to the server, the server checks to see if the token is valid, and you're done. This is much simpler to implement than OAuth 1.0a, but it is only secure if you use SSL for every request. Applications that won't or can't use SSL may still use the old way of transmitting each token, which encrypts the token so that it is safe even if SSL is not used or even if it is intercepted by a proxy like Apigee.
However, OAuth 2.0 is far from complete. It is currently undergoing lots of discussion on the IETF mailing list, and the spec draft changes daily.
That's why I was surprised to read today that Facebook is using OAuth 2.0 to authenticate its own API. Now, some of the key players in OAuth work at Facebook, and they have chosen to use only a part of the spec, and the part that's arguably the least complicated. I'm sure that they feel that taking this calculated risk now is in the best interest of Facebook and its developer community, but the possibility remains that the spec will change and Facebook will have to change its implementation to match.
(In fact, at the moment I write this, they do not -- the name of the query parameter that holds the token is "access_token" in the Facebook documentation and "oauth_token" in the latest version of the spec repository.)
In the meantime, developers building on top of these APIs may have to contend with OAuth 1.0a (the current spec), OAuth 1.0 (an older version that some sites may still use), the draft form of OAuth 2.0 as implemented by Facebook, and even "WRAP," which introduced some of the concepts used in OAuth 2.0.
So the good news is that there are lot of good standards being written that can make it easier to produce and consume powerful and secure APIs. The bad news is that those standards are still changing. So stay tuned, and be careful!