Secured web service (windows active directory auth) single sign-on through C#?

[D_R_]

Hi, I have a secured map service, which is secured using windows active directory (Web-tier authentication) info. I can access it using web browser by entering my credentials in default browser popup. No problems here.

But I have a need to create a custom web form which takes in windows active directory credentials and somehow lets secured ArcGIS web services know that I am signed-in already  I guess I must send back proper ArcGIS cookies to the client... And I have no idea where to get them.

Help would be much appreciated!