Developers, take a look at Vittorio Bertocci’s recent post Windows Azure Authentication Library: a Deep Dive , which begins like this: We are very excited today to announce our first developer preview of the Windows Azure Authentication Library (AAL). For an overview, please head to Alex’s announcement post on the Windows Azure blog: but in a nutshell, the Windows Azure Authentication Library (AAL) makes it very easy for developers to add to their client applications the logic for authenticating users to Windows Azure Active Directory or their providers of choice, and obtain access tokens for securing API calls. Furthermore, AAL helps service authors to secure their API by providing validation logic for incoming tokens. That’s the short version: below I will give you (much) more details. Vittorio more