Windows Azure AppFabric provides both an Enterprise Service Bus in the cloud as well as cloud based authentication and authorization (think federation – ala ADFS). There’s a good introduction to the AppFabric (here), but it uses the CTP version of the App Fabric SDK. It also took me awhile to figure out that I needed to install the AppFabric SDK separately from the Azure Development Tools install.
As I said, the training above on the AppFabric was done in December 09 on the CTP, so some things changed from then, including the location of the Microsoft.ServiceBus.dll file. In the CTP it was under the name of “Microsoft .NET Services SDK (November 2009 CTP)”, but the released version is available (on my 64-bit Windows 7 machine) under “C:\Program Files (x86)\Windows Azure platform AppFabric SDK\V1.0\Assemblies”
Hopefully next time I won’t have to search as hard.