如何在php中验证Google admob的SSV？

<?php
// 获取SSV验证参数
$ad_network = $_GET['ad_network'];
$ad_unit = $_GET['ad_unit'];
$timestamp = $_GET['timestamp'];
$transaction_id = $_GET['transaction_id'];
$user_id = $_GET['user_id'];
$signature = $_GET['signature'];

// 构建验证请求
$data = array(
    'ad_network' => $ad_network,
    'ad_unit' => $ad_unit,
    'timestamp' => $timestamp,
    'transaction_id' => $transaction_id,
    'user_id' => $user_id,
    'signature' => $signature
);

// 将数据编码为JSON格式
$json_data = json_encode($data);

// 设置验证URL和密钥
$verification_url = 'https://your-verification-url.com/verify'; // 替换为你的验证URL
$secret_key = 'your-secret-key'; // 替换为你的密钥

// 创建cURL请求
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $verification_url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $json_data);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Content-Type: application/json',
    'Authorization: Bearer ' . $secret_key
));

// 发送请求并获取响应
$response = curl_exec($ch);

// 关闭cURL请求
curl_close($ch);

// 处理验证响应
if ($response === false) {
    // 请求失败
    echo 'SSV验证请求失败';
} else {
    $response_data = json_decode($response, true);
    if ($response_data['success']) {
        // 验证成功
        echo 'SSV验证成功';
    } else {
        // 验证失败
        echo 'SSV验证失败';
    }
}
?>