This article is from the Secure Sockets Layer Discussion List FAQ, by Shannon Appel SAppel@consensus.com with numerous contributions by others.
Client authentication as implemented by Microsoft Internet Explorer
3.0 is interoperable with popular Web servers that support secure
sockets layer (SSL) 3.0 client authentication.
Internet Information Server 3.0 supports client authentication using
standards-based X.509 version 3 certificates. Webmasters can easily
add client authentication to their Web sites by creating an Active
Server Pages (ASP) application.