As you know there is no UI to configure iisClientCertificateMappingAuthentication in IIS7, it takes a little more time to configure the site for the same. Here is an article in the iis.net site which explains the steps one by one……………
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http://blogs.msdn.com/rakkimk/archive/2009/07/08/iis7-configuring-iisclientcertificatemappingauthentication.aspx