function transferSessionIdToCookieAndRedirect()
{
    $sessionId = getParameter("sessionId");
    if (isValidSessionId($sessionId)) {
        debug("setting session cookie");
        setcookie(COOKIE_SESSION_ID, $sessionId, time() + 60 * 60 * 24, "/", getDomainName());
        $baseUrl = getBaseUrl();
        debug("redirecting to: " . $baseUrl);
        header("Location: " . $baseUrl . "/");
    } else {
        performLogout();
    }
}
<?php

include "util/auth.php";
performLogout();