Desktop widget integration

Hi,recently i’m designing a desktop widget for my client,now the problem is my client wish to integrate the widget with his on going ee site currently developing by another programmer.He wish to use the same login details to login the widget so i’m wonder Is there an single sign on mechanism implement or available to use it with the session key?the desktop widget build on Adobe AIR for the UI and Dot NET(Framework 3.5) for the widget server.