使用salt和哈希密码更改pdo函数的登录脚本

Question

有谁知道如何更改下面的登录脚本以使用PDO功能？

$username = $_POST['username'];
$password = $_POST['password'];
//connect to the database here
$username = mysql_real_escape_string($username);
$query = "SELECT password, salt
        FROM users
        WHERE username = '$username';";
$result = mysql_query($query);
if(mysql_num_rows($result) < 1) //no such user exists
{
    header('Location: login_form.php');
}
$userData = mysql_fetch_array($result, MYSQL_ASSOC);
$hash = hash('sha256', $userData['salt'] . hash('sha256', $password) );
if($hash != $userData['password']) //incorrect password
{
    header('Location: login_form.php');
}
$_SESSION['logged_in'] = true;

我目前使用下面的脚本，但它使用md5，上面的脚本使用散列密码和盐。正如您所看到的，上面的脚本不使用PDO功能，因此每次都会收到错误消息。

if (isset($_POST['username'], $_POST['password'])) {
    $username = $_POST['username']; 
    $password = md5($_POST['password']);

    if (empty($username) or empty($password)) {
        $error = 'Who the hell are you?';

    }else {
        $query =$pdo->prepare("SELECT * FROM users WHERE user_name = ? AND user_password = ?");

        $query->bindvalue(1, $username);
        $query->bindvalue(2, $password);

        $query->execute();

        $num = $query->rowCOUNT();

        if ($num == 1) {
            $_SESSION['logged_in'] = true;

            header('Location: index2.php');

            exit();
        } else {

            $error = 'Wrong wrong wrong!';


        }


    }}

非常感谢任何帮助，谢谢！