Signing data with your private exchange key

[Alexi Delahousse]

Hello,

I am making an asp.net commerce site (with commerce server 2002 and
Visual Studio .Net 2003 ASP.NET C#).
I'm using user and server certificates with HttpClientCertificate, this is
working great.

Now I would like to know, how to ask the user to sign with his certificate a
"transaction".

The user must sign with his certificate when he's comming (in IIS specify,
access to the site require a user certificate)

If possible, I want to show the form "Signing data with your private
exchange key", same as user come's to the site, whenever i want.

Is that possible ?
With my research on the web , i found nothing

I thank you in advance