Question: Is it possible to use the built in ASP.NET membership provider to secure a web service?

I have a SQL Server database already setup with my membership and now I want to provide a web service that only members are allowed to use. Is it possible to authenticate against this (if so how?) or do I need to have a seperate type of authentication for the web services?

Answer: 
There actually is a solution, it turns out: WebRequest.PreAuthenticate
Check out an [article](http://www.west-wind.com/Weblog/posts/243915.aspx) by Rick Strahl.
This "double handshake" is a integral part of NTLM's challenge response model. Your only option would be to change the authentication type.

Alternatively, you try re-using the connection for web service calls.