Is there a built in procedure to digitally sign an HTTPS request with client's SSL private key in .net? Also, is there a built in procedure to verify the digital signature against an SSL certificate? Or do I have to roll my own? Or is there a third party library?

I need the request to be digitally signed because the client manipulates money, so I want to be sure that the request really comes from the client and that nobody tampers with the content of the request.

I'm also considering using SSL client certificate, but it can only provide confidentiality and authentication, but not data integrity.