I'm preparing to write a number of posts over the next week or two on the topic of authentication in ASP.NET AJAX; again going under the hood and exploring how the internals work as well as showing you all of the features of authentication (and how to best leverage it in your applications). I should have a post ready by tonight on the topic, but if you have any particular interests in this area feel free to comment on this post and I'll make sure to bring up your topic in this or the next couple articles.