I found an interesting Microsoft KB article today:
HOW TO: Create an IAuthenticationModule by Using Visual Basic .NET
Summary: This step-by-step article discusses how to use Visual Basic .NET to create an implementation of an IAuthenticationModule module that performs Basic authentication. This article describes how to create, deploy, configure, and then test the authentication module. An authentication module is a component that a client uses to perform authentication with the server. Applications that use the WebResponse class rely on the authentication module.
This is also very useful for unit testing using NUnitAsp!