Introducing ‘Sign-in with Twitter’, OAuth-Style “Connect” « hueniverse:

It is important to understand that there are two different kind of single-sign-on solutions: delegated and federated. All the recent comparisons between OpenID and Facebook Connect failed to appreciate this fundamental difference. Facebook Connect is a delegated authentication service, while OpenID is a federated authentication service. They might offer very similar features, but they are very different.

A delegated solution means that one site is simply outsourcing its authentication needs to another pre-selected site. If your site uses Facebook Connect, you are delegating your authentication facilities to Facebook. Visitors to your site cannot use any other accounts, only accounts from the vendors you have pre-selected.

A federated solution means that visitors to your site can use any account they have, as long as it is compatible. It makes no difference to the site which account is being used, as long as it can interoperate. At its core, OpenID is a federated solution because its most important feature is the ability to use any OpenID account with any OpenID-enabled service.

(Via @cshirky.)