如何将Google Business Messages的cURL OAuth2头转换为PHP cURL实现？

你提到的-H "$(oauth2l header --json ./service_account_key.json businessmessages)"本质是生成针对Google Business Messages API的OAuth2 Bearer授权头。oauth2l工具帮你完成了从服务账号密钥获取访问令牌的流程，在PHP里我们可以自己实现这个逻辑，不用依赖该工具。

方案一：使用Google PHP客户端库（推荐，更稳定） #

Google官方的google/apiclient库可以自动处理服务账号的令牌获取，避免手动编写复杂的JWT签名逻辑：

1. 先通过Composer安装依赖：

composer require google/apiclient

2. 编写代码获取令牌并发送回复：

<?php
require __DIR__ . '/vendor/autoload.php';

// 加载服务账号密钥文件
$client = new Google\Client();
$client->setAuthConfig('./service_account_key.json');
// 设置Business Messages的API权限范围
$client->addScope('https://www.googleapis.com/auth/businessmessages');
// 以服务账号身份请求令牌
$client->fetchAccessTokenWithAssertion();
$accessToken = $client->getAccessToken()['access_token'];

// 构造回复消息的请求体
$messagePayload = [
    'messageId' => uniqid('msg_'), // 生成唯一消息ID
    'text' => '这是来自PHP的回复消息',
    'representative' => [
        'avatarImage' => 'https://example.com/avatar.png', // 可选：客服头像URL
        'displayName' => '客服小助手'
    ]
];

// 目标对话ID（从入站消息的webhook请求体中获取）
$conversationId = 'YOUR_CONVERSATION_ID';
$apiUrl = "https://businessmessages.googleapis.com/v1/conversations/{$conversationId}/messages";

// 初始化cURL
$ch = curl_init($apiUrl);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($messagePayload));
// 设置请求头，包括授权头和Content-Type
curl_setopt($ch, CURLOPT_HTTPHEADER, [
    "Authorization: Bearer {$accessToken}",
    'Content-Type: application/json'
]);

// 执行请求并处理响应
$response = curl_exec($ch);
$httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);

if ($httpCode !== 200) {
    echo "请求失败，状态码：{$httpCode}，响应内容：{$response}";
} else {
    echo "消息发送成功，响应：{$response}";
}

curl_close($ch);
?>

方案二：纯cURL手动实现令牌获取（无需第三方库） #

如果不想依赖Composer包，可以手动生成JWT并请求访问令牌：

步骤1：生成JWT签名 #

需要使用服务账号密钥中的私钥，以RS256算法生成JWT：

<?php
function generateJwt($serviceAccountKey) {
    $header = json_encode(['alg' => 'RS256', 'typ' => 'JWT']);
    $now = time();
    $payload = json_encode([
        'iss' => $serviceAccountKey['client_email'],
        'scope' => 'https://www.googleapis.com/auth/businessmessages',
        'aud' => 'https://oauth2.googleapis.com/token',
        'exp' => $now + 3600, // 令牌有效期1小时
        'iat' => $now
    ]);

    // 编码成Base64URL格式
    $base64Header = str_replace(['+', '/', '='], ['-', '_', ''], base64_encode($header));
    $base64Payload = str_replace(['+', '/', '='], ['-', '_', ''], base64_encode($payload));

    // 用私钥签名
    $signature = '';
    openssl_sign($base64Header . '.' . $base64Payload, $signature, $serviceAccountKey['private_key'], OPENSSL_ALGO_SHA256);
    $base64Signature = str_replace(['+', '/', '='], ['-', '_', ''], base64_encode($signature));

    return $base64Header . '.' . $base64Payload . '.' . $base64Signature;
}
?>

步骤2：获取访问令牌并发送消息 #

<?php
// 加载服务账号密钥
$serviceAccountKey = json_decode(file_get_contents('./service_account_key.json'), true);
$jwt = generateJwt($serviceAccountKey);

// 请求访问令牌
$tokenUrl = 'https://oauth2.googleapis.com/token';
$tokenPayload = http_build_query([
    'grant_type' => 'urn:ietf:params:oauth:grant-type:jwt-bearer',
    'assertion' => $jwt
]);

$tokenCh = curl_init($tokenUrl);
curl_setopt($tokenCh, CURLOPT_RETURNTRANSFER, true);
curl_setopt($tokenCh, CURLOPT_POST, true);
curl_setopt($tokenCh, CURLOPT_POSTFIELDS, $tokenPayload);
$tokenResponse = json_decode(curl_exec($tokenCh), true);
curl_close($tokenCh);

if (!isset($tokenResponse['access_token'])) {
    die('获取令牌失败：' . json_encode($tokenResponse));
}
$accessToken = $tokenResponse['access_token'];

// 构造并发送回复消息
$conversationId = 'YOUR_CONVERSATION_ID';
$apiUrl = "https://businessmessages.googleapis.com/v1/conversations/{$conversationId}/messages";
$messagePayload = [
    'messageId' => uniqid('msg_'),
    'text' => '纯cURL实现的回复消息',
    'representative' => [
        'displayName' => 'PHP客服'
    ]
];

$ch = curl_init($apiUrl);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($messagePayload));
curl_setopt($ch, CURLOPT_HTTPHEADER, [
    "Authorization: Bearer {$accessToken}",
    'Content-Type: application/json'
]);

$response = curl_exec($ch);
$httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);

echo $httpCode === 200 ? "发送成功：{$response}" : "失败，状态码{$httpCode}：{$response}";
curl_close($ch);
?>

关键注意事项 #

• 确保服务账号已被授予Google Business Messages的相关权限，并且已关联到你的商家账号。
• conversationId需要从入站消息的Webhook请求体中获取（通常在conversation.id字段）。
• 令牌有效期为1小时，建议缓存令牌避免重复请求。

内容的提问来源于stack exchange，提问作者Phil Barnes