Custom RIA Authentication

Question

Following the steps in this post: http://forums.silverlight.net/forums/t/177042.aspx

Where/How do I add the [Key] attribute on the Name property of the IAuthentication where User is one of my ADO.Net Entity objects?

My options so far seem to be:

• In the designer codebehind of me ADO.Net Entity Model.
• Create a partial User class and add it there
• In the AuthenticationService.metadata.cs partial User class.

It just does not seem to work no matter where I place the [Key] attribute.