attach certificate

[maddy41]

I have this code working to a point it posts an xml file to a server however i have to present my digital certificate to the server and dont know how to do this does any one know wher i start?
any direction would be greate.

_____________working_code________________________
Dim responsestr As String
Dim strURL As String = "

https://website/PortalServlet"

Dim xmlPath As String = "C:\message.xml"
Dim xmlDoc As New MSXML2.DOMDocument40
Dim xmlHTTP As New MSXML2.ServerXMLHTTP40
If xmlDoc.load(xmlPath) Then
'Set method, url, async
xmlHTTP.open("POST", strURL, False)
'Send XML document
xmlHTTP.send(xmlDoc.xml)
responsestr = xmlHTTP.responseText
MessageBox.Show(xmlHTTP.responseText)
End If