If using Windows Authentication with IIS PHP can read the current authenticated user thats logged on from $_SERVER["LOGON_USER"];
If this is set and the user is not getting a HTTP auth prompt you can assume the user credentials are correct. So with some WP coding you could read that $_SERVER['LOGON_USER']
and if not logged into WP auto log them in with that username.
place in theme functions file or in a MU plugins file.
function auto_login() {
if (!is_user_logged_in() && isset($_SERVER['LOGON_USER'])) {
$user_login = $_SERVER['LOGON_USER'];
$user = get_userdatabylogin($user_login);
$user_id = $user->ID;
wp_set_current_user($user_id, $user_login);
wp_set_auth_cookie($user_id);
do_action('wp_login', $user_login);
}
}
add_action('init', 'auto_login');
You may need to do some further tweaking to the $user_login
variable so that you get the correct username that matches in the WP table.