Authenticating to web service using https and client certificate

[jakecjacobson]

Hi,

I need to post some XML files to a web client that requires a client
certificate to authenticate.  I have some code that works on posting a
multipart form over http but I need to modify it to pass the proper
certificate and post the XML file.  Is there any example code that
will point me in the correct direction?  Thanks for your help.