PHP和Active Directory身份验证允许错误的密码

我正在我们的内部站点中使用Active Directory进行身份验证。但是，如果你输入了错误的密码，它找到了用户名，它仍然允许身份验证。所以基本上，这告诉我，它甚至没有真正检查密码是否匹配。有没有一种方法可以确保进行实际的身份验证？

<?php session_start();
include '_includes/header.php';
// form defaults
$error['alert'] = '';
$error['user']  = '';
$error['pass']  = '';
$input['user']  = '';
$input['pass']  = '';

if(isset($_POST['submit']))
{
    if($_POST['username'] == '' || $_POST['password'] == '')
    {
        if($_POST['username'] == '') { $error['user'] = 'required!'; }
        if($_POST['password'] == '') { $error['pass'] = 'required!'; }
        $error['alert'] = 'Please fill in the required fields';
        $input['user'] = htmlentities($_POST['username'], ENT_QUOTES);
        $input['pass'] = htmlentities($_POST['password'], ENT_QUOTES);
        include 'views/v_authentication.php';
    }
    else
    {
        $input['user'] = htmlentities($_POST['username'], ENT_QUOTES);
        $input['pass'] = htmlentities($_POST['password'], ENT_QUOTES);
        $user = $input['user'] . '@domain.local';
        $ldap = ldap_connect("name.of.ldap.server");
        if($bind = ldap_bind($ldap, $user, $pass)) {
            $_SESSION['id'] = $id;
            $_SESSION['type'] = $type;
            $_SESSION['username'] = $input['user'];
            $_SESSION['last_active'] = time();
            header('Location: index.php');
        } else {
                // username/password incorrect
            $error['alert'] = "Username or password incorrect!";
            include 'views/v_authentication.php';
        }
    }
}
else
{
    // check for any variables within the URL
    if (isset($_GET['unauthorized']))
    {
        $error['alert'] = 'Please login to view that page!';
    }
    if (isset($_GET['timeout']))
    {
        $error['alert'] = 'Your session has expired. Please log in again.';
    }
    // if the form hasn't been submitted, show form
    include 'views/v_authentication.php';
}
$ldap->close();
 ?>
 <?php include 'views/v_authentication.php'; ?>
 <?php include '_includes/footer.php'; ?>