Are SSL client certificates supported ?
Both SslClientStream and SslServerStream, in Mono.Security.dll, support client certificates, however HttpWebRequest doesn’t due to a strange design/relationship between the 1.x framework and Windows/CryptoAPI (i.e. there is no managed API to associate a certificate with a private key). This should be fixed in the 2.0 profile as the X509Certificate class has been extended to provide this association. Also recent versions of XSP (http://www.mono-project.com/ASP.NET#XSP) do support SSL/TLS and client certificates. See the UsingClientCertificatesWithXSP article for more details.