验证服务器端的 Google ID 令牌

Google 返回 ID 令牌后，系统会通过 HTTP POST 方法请求（参数名称为 credential）将该令牌提交到您的登录端点。

以下是一个 Python 语言示例，显示了验证和使用 ID 令牌的常规步骤：

验证跨站请求伪造 (CSRF) 令牌。当您将凭据提交到登录端点时，我们会使用双重提交 Cookie 模式来防止 CSRF 攻击。每次提交前，我们都会生成令牌。然后，将令牌同时放入 Cookie 和 post 正文，如以下代码示例所示：

csrf_token_cookie = self.request.cookies.get('g_csrf_token')
if not csrf_token_cookie:
    webapp2.abort(400, 'No CSRF token in Cookie.')
csrf_token_body = self.request.get('g_csrf_token')
if not csrf_token_body:
    webapp2.abort(400, 'No CSRF token in post body.')
if csrf_token_cookie != csrf_token_body:
    webapp2.abort(400, 'Failed to verify double submit cookie.')

验证 ID 令牌。

如需验证令牌是否有效，请确保：满足条件：
- ID 令牌已由 Google 正确签名。使用 Google 的公钥（适用于 JWK 或 PEM 格式）以验证令牌的签名。这些密钥会定期轮替：检查响应中的 Cache-Control 标头来确定何时您应该再次检索它们。
- ID 令牌中 aud 的值等于您应用的某个客户端 ID必须进行此检查，以防止向恶意应用用于访问应用的后端服务器上的同一用户的相关数据。
- ID 令牌中 iss 的值等于 accounts.google.com 或 https://accounts.google.com。
- ID 令牌的过期时间 (exp) 未过。
- 如果您需要验证 ID 令牌是否代表 Google Workspace 或 Cloud 组织账号时，您可以查看 hd 声明，该声明表示托管的用户的网域。将资源访问权限限制为只有特定网域。缺少此声明即表示相应账号不属于 Google 托管的域名。
您可以使用 email、email_verified 和 hd 字段来确定 Google 负责托管电子邮件地址，并对其具有权威性。如果 Google 拥有权威性，该用户就是所知的合法账号所有者，您可以跳过密码或其他输入框验证方法。

Google 具有权威性的情形：
- email 的后缀为 @gmail.com，这是一个 Gmail 账号。
- email_verified 为 true 且 hd 已设置，这是 G Suite 账号。
用户无需使用 Gmail 或 G Suite 即可注册 Google 账号。时间 email 不包含 @gmail.com 后缀且 hd 不存在，Google 未建议使用权威凭据和密码或其他验证方法进行验证用户。email_verified 可能为 true，因为 Google 最初验证了创建 Google 账号后，该用户会拥有第三方的所有权，后，电子邮件账号可能已更改。

我们强烈建议不要自行编写代码来执行这些验证步骤，建议您使用适用于您平台的 Google API 客户端库， JWT 库。对于开发和调试，您可以调用我们的 tokeninfo 验证端点。

Using a Google API Client Library

Using one of the Google API Client Libraries (e.g. Java, Node.js, PHP, Python) is the recommended way to validate Google ID tokens in a production environment.
Java

To validate an ID token in Java, use the GoogleIdTokenVerifier object. For example:
```
import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken;
import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken.Payload;
import com.google.api.client.googleapis.auth.oauth2.GoogleIdTokenVerifier;

...

GoogleIdTokenVerifier verifier = new GoogleIdTokenVerifier.Builder(transport, jsonFactory)
    // Specify the CLIENT_ID of the app that accesses the backend:
    .setAudience(Collections.singletonList(CLIENT_ID))
    // Or, if multiple clients access the backend:
    //.setAudience(Arrays.asList(CLIENT_ID_1, CLIENT_ID_2, CLIENT_ID_3))
    .build();

// (Receive idTokenString by HTTPS POST)

GoogleIdToken idToken = verifier.verify(idTokenString);
if (idToken != null) {
  Payload payload = idToken.getPayload();

  // Print user identifier
  String userId = payload.getSubject();
  System.out.println("User ID: " + userId);

  // Get profile information from payload
  String email = payload.getEmail();
  boolean emailVerified = Boolean.valueOf(payload.getEmailVerified());
  String name = (String) payload.get("name");
  String pictureUrl = (String) payload.get("picture");
  String locale = (String) payload.get("locale");
  String familyName = (String) payload.get("family_name");
  String givenName = (String) payload.get("given_name");

  // Use or store profile information
  // ...

} else {
  System.out.println("Invalid ID token.");
}
```
The GoogleIdTokenVerifier.verify() method verifies the JWT signature, the aud claim, the iss claim, and the exp claim.

If you need to validate that the ID token represents a Google Workspace or Cloud organization account, you can verify the hd claim by checking the domain name returned by the Payload.getHostedDomain() method. The domain of the email claim is insufficient to ensure that the account is managed by a domain or organization.
Node.js

To validate an ID token in Node.js, use the Google Auth Library for Node.js. Install the library:
```
npm install google-auth-library --save
```
Then, call the verifyIdToken() function. For example:
```
const {OAuth2Client} = require('google-auth-library');
const client = new OAuth2Client();
async function verify() {
  const ticket = await client.verifyIdToken({
      idToken: token,
      audience: CLIENT_ID,  // Specify the CLIENT_ID of the app that accesses the backend
      // Or, if multiple clients access the backend:
      //[CLIENT_ID_1, CLIENT_ID_2, CLIENT_ID_3]
  });
  const payload = ticket.getPayload();
  const userid = payload['sub'];
  // If the request specified a Google Workspace domain:
  // const domain = payload['hd'];
}
verify().catch(console.error);
```
The verifyIdToken function verifies the JWT signature, the aud claim, the exp claim, and the iss claim.

If you need to validate that the ID token represents a Google Workspace or Cloud organization account, you can check the hd claim, which indicates the hosted domain of the user. This must be used when restricting access to a resource to only members of certain domains. The absence of this claim indicates that the account does not belong to a Google hosted domain.
PHP

To validate an ID token in PHP, use the Google API Client Library for PHP. Install the library (for example, using Composer):
```
composer require google/apiclient
```
Then, call the verifyIdToken() function. For example:
```
require_once 'vendor/autoload.php';

// Get $id_token via HTTPS POST.

$client = new Google_Client(['client_id' => $CLIENT_ID]);  // Specify the CLIENT_ID of the app that accesses the backend
$payload = $client->verifyIdToken($id_token);
if ($payload) {
  $userid = $payload['sub'];
  // If the request specified a Google Workspace domain
  //$domain = $payload['hd'];
} else {
  // Invalid ID token
}
```
The verifyIdToken function verifies the JWT signature, the aud claim, the exp claim, and the iss claim.

If you need to validate that the ID token represents a Google Workspace or Cloud organization account, you can check the hd claim, which indicates the hosted domain of the user. This must be used when restricting access to a resource to only members of certain domains. The absence of this claim indicates that the account does not belong to a Google hosted domain.
Python

To validate an ID token in Python, use the verify_oauth2_token function. For example:
```
from google.oauth2 import id_token
from google.auth.transport import requests

# (Receive token by HTTPS POST)
# ...

try:
    # Specify the CLIENT_ID of the app that accesses the backend:
    idinfo = id_token.verify_oauth2_token(token, requests.Request(), CLIENT_ID)

    # Or, if multiple clients access the backend server:
    # idinfo = id_token.verify_oauth2_token(token, requests.Request())
    # if idinfo['aud'] not in [CLIENT_ID_1, CLIENT_ID_2, CLIENT_ID_3]:
    #     raise ValueError('Could not verify audience.')

    # If the request specified a Google Workspace domain
    # if idinfo['hd'] != DOMAIN_NAME:
    #     raise ValueError('Wrong domain name.')

    # ID token is valid. Get the user's Google Account ID from the decoded token.
    userid = idinfo['sub']
except ValueError:
    # Invalid token
    pass
```
The verify_oauth2_token function verifies the JWT signature, the aud claim, and the exp claim. You must also verify the hd claim (if applicable) by examining the object that verify_oauth2_token returns. If multiple clients access the backend server, also manually verify the aud claim.
要点：ID 令牌在 credential 字段（而非 g_csrf_token 字段）中返回。
确认令牌的有效性后，您可以使用 Google ID 令牌中的信息将您网站的帐号状态关联起来：
- 未注册用户：您可以显示一个注册界面，以便用户根据需要提供额外的个人资料信息。它还允许用户以静默方式创建新帐号和已登录的用户会话。
- 网站中已存在的现有帐号：您可以显示一个网页，供最终用户输入密码并将旧版帐号与其 Google 凭据相关联。这将确认用户有权访问现有帐号。
- 回访联合用户：您可以让用户以静默方式登录。

验证服务器端的 Google ID 令牌

Using a Google API Client Library