How to setup RIA Services to use an existing ASP.Net membership base

[P]

I'd like to make an OOB Silverlight app based on the Silverlight Business Application template in Visual Studio. The template uses the default ASP.Net membership provider. I understand how to use that to add users and roles, etc. I've found plenty of tutorials on that. What I'd like to be able to do, is configure the Silverlight template so that it uses an existing ASP.Net membership base. We'd like this app to have a companion website (ASP.Net based).To clarify: We've been able to setup an ASP.Net website and have created a SQL database with the required tables (aspnet_Users, aspnet_Membership, etc.). I'd like to configure a Silverlight app to access the same users and roles that are in those tables.Can anyone help me out in terms of what I'd need to put in the Web.config? Do I just need a connection string? I'm new to ASP.Net authentication, but I'd rather use what ASP.Net gives me out of the box than have to write my own authentication service. I feel like this should be really easy, and is just a matter of pointing the Silverlight app in the right direction.I'd like to use Silverlight 5 and .Net 4.5 if I can but I don't mind using an older version of either if it makes things easier.