基本身份验证在localhost中有效，但在生产服务器中失败

我在PHP、中有以下代码

<?php
ob_start();
$valid_passwords = array ("matrixUlt" => "$ecurEh1FIVE");
$valid_users = array_keys($valid_passwords);
$user = $pass = null;
if(isset($_SERVER['PHP_AUTH_USER']) && isset($_SERVER['PHP_AUTH_PW']))
{
    $user = $_SERVER['PHP_AUTH_USER'];
    $pass = $_SERVER['PHP_AUTH_PW'];
}
$validated = (in_array($user, $valid_users)) && ($pass == $valid_passwords[$user]);
if(!$validated)
{
header('WWW-Authenticate: Basic realm="You need to be authenticated to access the resource!"');
header('HTTP/1.0 401 Unauthorized');
exit("Not authorized");
echo ob_get_clean();
}

当给出[（"matrixUlt"=>"$ecurEH15VE"]用户名：密码时，这在localhost中正常工作。但在LIVE服务器/生产环境中不断显示身份验证对话框。有什么想法吗？