if ($_SERVER['HTTPS'] != 'on') {
    // HTTP
    if ($_COOKIE[COOK_SECURED]) {
            // redirect back to https
            $url = 'https://' . $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'];
            header("Location: $url");
            exit;
    }
    session_set_cookie_params(COOK_LIFE, COOK_PATH, COOK_DOM, false);
    session_start();

else {
    // HTTPS
    session_set_cookie_params(COOK_LIFE, COOK_PATH, COOK_DOM, true);
    session_start();
    if (!isset($_SESSION[SESS_OLD_ID])) {
       
        $old_sessionid = session_id();
       
        $ss = session_encode();
       
        session_regenerate_id(true);
       
        session_decode($ss);
       
        $_SESSION[SESS_OLD_ID] = $old_sessionid;
        setcookie(COOK_SECURED, 1);
    }
}

if (isset($_SESSION[SESS_OLD_ID])) {
    session_unset();
    session_destroy();
    if (isset($_COOKIE['PHPSESSID'])) setcookie('PHPSESSID', '', time()-100, COOK_PATH, COOK_DOM);
    if (isset($_COOKIE[COOK_SECURED])) setcookie(COOK_SECURED, '', time()-100, COOK_PATH, COOK_DOM);
   
    $url = 'http://' . $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'];
    header("Location: $url");
}