Have a look at John's article
User Login For WinForm Applications[
^]
Basically, the magic is in these lines
WindowsIdentity identity = WindowsIdentity.GetCurrent();
WindowsPrincipal principal = new WindowsPrincipal(identity);
That will get you the current logged on user. You can then test for group membership and grant or deny access to resource based on membership
WindowsIdentity identity = WindowsIdentity.GetCurrent();
WindowsPrincipal principal = new WindowsPrincipal(identity);
if (principal.IsInRole("Administrator")
{
}
Try googling 'Winforms Windows Authentication' for more references