I’ve been scratching my head on this one yesterday. I wanted to use some kind of custom authentication with RIA Services instead of using the default one. The overview document found here states this:
If the Application Developer wants to use their own Custom Authentication, they can do so by implementing IAuthentication<User> instead of deriving from Authentication Base.
Well, I wasn’t able to get it to work so I fired up a quick email to Laurent Duveau who pointed me to this StackOverflow page where Nick Gotch explains how he did it simply by overriding some of the AuthenticationBase methods. Works like a charm!