Arnold Daniels has a new post to his blog today dealing with something (usually companies) are looking towards to help deal with the infamous "too many passwords for too many places" issue - a simple single sign-on tool that can be dropped in an used anywhere.

Associated websites often share user information, so a visitor only has to register once and can use that username and password for all sites. A good example for this is Google. [...] There are many single sign-on applications and protocols. Most of these are fairly complex. [...] I've written a simple single sign-on solution (400 lines of code), which works by linking sessions. This solutions works for normal websites as well as AJAX sites.

He compares the flow on a non-single sign-on site (lots of fetching between the client/server) and the first/following visits with his tool in place. You can download the source here (as well as the Ajax broker).