Hi there,
You won't find it as it's part of Visual Studio, not part of ASP.NET. You have at least three options to work around this:
1. Look for a commercial component vendor that sells ready-made solutions
2. Build your own using the Membership and RoleManager APIs
3. Take a look at this multi-part article series to get a ready-made solution with source:
http://msdn.microsoft.com/en-us/library/aa478958.aspx
Cheers,
Imar