透過後端伺服器驗證

如果您使用 Google 登入的應用程式或網站會與後端伺服器通訊，可能需要在伺服器上識別目前登入的使用者。為確保安全性，請在使用者順利登入後，使用 HTTPS 將使用者的 ID 權杖傳送至伺服器。接著，在伺服器上驗證完整性 並使用權杖內的使用者資訊建立 建立工作階段或建立新帳戶。

警告：請勿在後端伺服器上接受純使用者 ID，例如您可以透過 GoogleSignInAccount.getId() method 取得的 ID。經過修改的用戶端應用程式可以將任意使用者 ID 傳送至伺服器，以便冒用使用者身分，因此您必須改用可驗證的 ID 權杖，才能在伺服器端安全地取得已登入使用者的使用者 ID。

將 ID 權杖傳送至伺服器

首先，在使用者登入時取得 ID 權杖：

1. 當您 設定 Google 登入， 呼叫 requestIdToken 然後將 伺服器的網路用戶端 ID。

   // Request only the user's ID token, which can be used to identify the
   // user securely to your backend. This will contain the user's basic
   // profile (name, profile picture URL, etc) so you should not need to
   // make an additional call to personalize your application.
   GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
           .requestIdToken(getString(R.string.server_client_id))
           .requestEmail()
           .build();

2. 應用程式啟動時，請檢查使用者是否已透過 Google 登入應用程式， 呼叫 silentSignIn 來在這部裝置上或其他裝置：

   GoogleSignIn.silentSignIn()
       .addOnCompleteListener(
           this,
           new OnCompleteListener<GoogleSignInAccount>() {
             @Override
             public void onComplete(@NonNull Task<GoogleSignInAccount> task) {
               handleSignInResult(task);
             }
           });

3. 如果使用者無法在背景登入，請呈現正常的登出體驗，讓使用者選擇登入。使用者執行動作時 簽名 in，請在活動中取得使用者的 GoogleSignInAccount 登入意圖的結果：

   // This task is always completed immediately, there is no need to attach an
   // asynchronous listener.
   Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
   handleSignInResult(task);

4. 在使用者以靜默或明確方式登入後，請從 GoogleSignInAccount 物件取得 ID 權杖：

   private void handleSignInResult(@NonNull Task<GoogleSignInAccount> completedTask) {
       try {
           GoogleSignInAccount account = completedTask.getResult(ApiException.class);
           String idToken = account.getIdToken();
   
           // TODO(developer): send ID Token to server and validate
   
           updateUI(account);
       } catch (ApiException e) {
           Log.w(TAG, "handleSignInResult:error", e);
           updateUI(null);
       }
   }

   如果您未使用 requestIdToken 設定 GoogleSignInOptions，getIdToken 會傳回 null。

接著，請透過 HTTPS POST 要求將 ID 權杖傳送至伺服器：

HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost("https://yourbackend.example.com/tokensignin");

try {
  List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
  nameValuePairs.add(new BasicNameValuePair("idToken", idToken));
  httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

  HttpResponse response = httpClient.execute(httpPost);
  int statusCode = response.getStatusLine().getStatusCode();
  final String responseBody = EntityUtils.toString(response.getEntity());
  Log.i(TAG, "Signed in as: " + responseBody);
} catch (ClientProtocolException e) {
  Log.e(TAG, "Error sending ID token to backend.", e);
} catch (IOException e) {
  Log.e(TAG, "Error sending ID token to backend.", e);
}

驗證 ID 權杖的完整性

透過 HTTPS POST 接收 ID 權杖後，您必須驗證權杖的完整性。

To verify that the token is valid, ensure that the following criteria are satisfied:

• The ID token is properly signed by Google. Use Google's public keys (available in JWK or PEM format) to verify the token's signature. These keys are regularly rotated; examine the Cache-Control header in the response to determine when you should retrieve them again.
• The value of aud in the ID token is equal to one of your app's client IDs. This check is necessary to prevent ID tokens issued to a malicious app being used to access data about the same user on your app's backend server.
• The value of iss in the ID token is equal to accounts.google.com or https://accounts.google.com.
• The expiry time (exp) of the ID token has not passed.
• 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.

Using the email, email_verified and hd fields, you can determine if Google hosts and is authoritative for an email address. In the cases where Google is authoritative, the user is known to be the legitimate account owner, and you may skip password or other challenge methods.

Cases where Google is authoritative:

• email has a @gmail.com suffix, this is a Gmail account.
• email_verified is true and hd is set, this is a Google Workspace account.

Users may register for Google Accounts without using Gmail or Google Workspace. When email does not contain a @gmail.com suffix and hd is absent, Google is not authoritative and password or other challenge methods are recommended to verify the user. email_verified can also be true as Google initially verified the user when the Google account was created, however ownership of the third party email account may have since changed.

Rather than writing your own code to perform these verification steps, we strongly recommend using a Google API client library for your platform, or a general-purpose JWT library. For development and debugging, you can call our tokeninfo validation endpoint.

使用 Google API 用戶端程式庫

使用其中一個 Google API 用戶端程式庫 (例如 Java、 Node.js、 PHP、 Python) 是在正式環境中驗證 Google ID 權杖的建議做法。

Java

如要在 Java 中驗證 ID 符記，請使用 GoogleIdTokenVerifier物件。例如：

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 WEB_CLIENT_ID of the app that accesses the backend:
    .setAudience(Collections.singletonList(WEB_CLIENT_ID))
    // Or, if multiple clients access the backend:
    //.setAudience(Arrays.asList(WEB_CLIENT_ID_1, WEB_CLIENT_ID_2, WEB_CLIENT_ID_3))
    .build();

// (Receive idTokenString by HTTPS POST)

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

  // Print user identifier. This ID is unique to each Google Account, making it suitable for
  // use as a primary key during account lookup. Email is not a good choice because it can be
  // changed by the user.
  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.");
}

GoogleIdTokenVerifier.verify() 方法會驗證 JWT 簽章、aud 宣告、iss 憑證和 exp著作權聲明。

如需驗證 ID 權杖是否代表 Google Workspace 或 Cloud 機構帳戶，您可以藉由檢查網域名稱來驗證 hd 擁有權聲明 是由 Payload.getHostedDomain() 方法傳回的。網域 email 憑證附加資訊不足以確保帳戶是由網域管理 或機構

，瞭解如何調查及移除這項存取權。

Node.js

如要透過 Node.js 驗證 ID 權杖，請使用 Node.js 適用的 Google 驗證程式庫。 安裝程式庫：

npm install google-auth-library --save

敬上 然後呼叫 verifyIdToken() 函式。例如：

const {OAuth2Client} = require('google-auth-library');
const client = new OAuth2Client();
async function verify() {
  const ticket = await client.verifyIdToken({
      idToken: token,
      audience: WEB_CLIENT_ID,  // Specify the WEB_CLIENT_ID of the app that accesses the backend
      // Or, if multiple clients access the backend:
      //[WEB_CLIENT_ID_1, WEB_CLIENT_ID_2, WEB_CLIENT_ID_3]
  });
  const payload = ticket.getPayload();
  // This ID is unique to each Google Account, making it suitable for use as a primary key
  // during account lookup. Email is not a good choice because it can be changed by the user.
  const userid = payload['sub'];
  // If the request specified a Google Workspace domain:
  // const domain = payload['hd'];
}
verify().catch(console.error);

verifyIdToken 函式會驗證 JWT 簽名、aud 憑證附加資訊、exp 憑證附加資訊 和 iss 聲明

如需驗證 ID 權杖是否代表 Google Workspace 或 Cloud 機構帳戶，您可以檢查 hd 憑證附加資訊，也就是 使用者的網域將資源存取權授予僅限成員時，就必須使用這個引數 無法歸類到特定網域沒有出現這項聲明，表示帳戶不屬於該帳戶所有 Google 代管的網域

，瞭解如何調查及移除這項存取權。

PHP

如要在 PHP 中驗證 ID 符記，請使用 PHP 適用的 Google API 用戶端程式庫。 安裝程式庫 (例如使用 Composer)：

composer require google/apiclient

敬上 然後呼叫 verifyIdToken() 函式。例如：

require_once 'vendor/autoload.php';

// Get $id_token via HTTPS POST.

$client = new Google_Client(['client_id' => $WEB_CLIENT_ID]);  // Specify the WEB_CLIENT_ID of the app that accesses the backend
$payload = $client->verifyIdToken($id_token);
if ($payload) {
  // This ID is unique to each Google Account, making it suitable for use as a primary key
  // during account lookup. Email is not a good choice because it can be changed by the user.
  $userid = $payload['sub'];
  // If the request specified a Google Workspace domain
  //$domain = $payload['hd'];
} else {
  // Invalid ID token
}

verifyIdToken 函式會驗證 JWT 簽名、aud 憑證附加資訊、exp 憑證附加資訊 和 iss 聲明

如需驗證 ID 權杖是否代表 Google Workspace 或 Cloud 機構帳戶，您可以檢查 hd 憑證附加資訊，也就是 使用者的網域將資源存取權授予僅限成員時，就必須使用這個引數 無法歸類到特定網域沒有出現這項聲明，表示帳戶不屬於該帳戶所有 Google 代管的網域

，瞭解如何調查及移除這項存取權。

Python

如要在 Python 中驗證 ID 符記，請使用 verify_oauth2_token 函式。例如：

from google.oauth2 import id_token
from google.auth.transport import requests

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

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

    # Or, if multiple clients access the backend server:
    # idinfo = id_token.verify_oauth2_token(token, requests.Request())
    # if idinfo['aud'] not in [WEB_CLIENT_ID_1, WEB_CLIENT_ID_2, WEB_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.
    # This ID is unique to each Google Account, making it suitable for use as a primary key
    # during account lookup. Email is not a good choice because it can be changed by the user.
    userid = idinfo['sub']
except ValueError:
    # Invalid token
    pass

verify_oauth2_token 函式會驗證 JWT 簽章、aud 聲明和 exp 聲明。 並驗證hd 來識別請求 (如果適用的話) 來檢查 會傳回 verify_oauth2_token。如果多位用戶端存取 後端伺服器，也手動驗證 aud 憑證附加資訊。

Calling the tokeninfo endpoint

An easy way to validate an ID token signature for debugging is to use the tokeninfo endpoint. Calling this endpoint involves an additional network request that does most of the validation for you while you test proper validation and payload extraction in your own code. It is not suitable for use in production code as requests may be throttled or otherwise subject to intermittent errors.

To validate an ID token using the tokeninfo endpoint, make an HTTPS POST or GET request to the endpoint, and pass your ID token in the id_token parameter. For example, to validate the token "XYZ123", make the following GET request:

https://oauth2.googleapis.com/tokeninfo?id_token=XYZ123

If the token is properly signed and the iss and exp claims have the expected values, you will get a HTTP 200 response, where the body contains the JSON-formatted ID token claims. Here's an example response:

{
 // These six fields are included in all Google ID Tokens.
 "iss": "https://accounts.google.com",
 "sub": "110169484474386276334",
 "azp": "1008719970978-hb24n2dstb40o45d4feuo2ukqmcc6381.apps.googleusercontent.com",
 "aud": "1008719970978-hb24n2dstb40o45d4feuo2ukqmcc6381.apps.googleusercontent.com",
 "iat": "1433978353",
 "exp": "1433981953",

 // These seven fields are only included when the user has granted the "profile" and
 // "email" OAuth scopes to the application.
 "email": "[e-mail]",
 "email_verified": "true",
 "name" : "Test User",
 "picture": "https://lh4.googleusercontent.com/-kYgzyAWpZzJ/ABCDEFGHI/AAAJKLMNOP/tIXL9Ir44LE/s99-c/photo.jpg",
 "given_name": "Test",
 "family_name": "User",
 "locale": "en"
}

Warning: Once you get these claims, you still need to check that the aud claim contains one of your app's client IDs. If it does, then the token is both valid and intended for your client, and you can safely retrieve and use the user's unique Google ID from the sub claim.

If you need to validate that the ID token represents a Google Workspace 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 Workspace hosted domain.

建立帳戶或工作階段

驗證權杖後，請檢查使用者是否已在使用者資料庫中。如果是的話，請為使用者建立已驗證的工作階段。如果使用者尚未在使用者資料庫中，請根據 ID 權杖酬載中的資訊建立新的使用者記錄，並為使用者建立工作階段。您可以提示 要求使用者在偵測到 新建立的使用者

保護使用者帳戶採用跨帳戶防護功能

只要您仰賴 Google 登入使用者，就能自動享有 安全功能和基礎架構，這是 Google 為了保護使用者資料而打造。不過 萬一使用者的 Google 帳戶遭到入侵，或發生其他 重大安全性事件，您的應用程式也較容易受到攻擊。為進一步保護帳戶免於遭受任何重大安全事件的影響，請使用跨帳戶保護功能，接收 Google 發出的安全警報。收到這些活動後，您 掌握使用者的 Google 帳戶安全性重大異動 即可對你的服務採取行動來保護帳戶安全。