Smartcard authentication in a multi-tier application

Hi,

We have a multi-tier intranet application. The users of this
application are windows users. We have a login screen on the client
side where the user enters the username and password and on the server
we use the function LogOnUser() to authenticte this user. We get the
SID of this user and the SID plays a major part in the businees
context of the application.

We are planning to allow the user to use the smart card as well in the
new version. I was just wondering how to go about with the
implementation as we need the domain username and password of the PIN-
authenticated smartcard user.

Generally what is the best design to use smartcard in a multi-tier
application which needs to be authentiacted on the server side?

Any suggestion on implementing this would be of great help.

Thanks
.