在您的服務器端驗證 Google ID 令牌

谷歌返回一個ID令牌後，它是由一個HTTP提交的POST方法請求，用參數名credential ，以您的登錄端點。

以下是 Python 語言中的示例，顯示了驗證和使用 ID 令牌的常用步驟：

1. 驗證跨站點請求偽造 (CSRF) 令牌。當您向登錄端點提交憑據時，我們使用雙重提交 cookie 模式來防止 CSRF 攻擊。在每次提交之前，我們都會生成一個令牌。然後，將令牌放入 cookie 和帖子正文中，如以下代碼示例所示：

   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.')
   

2. 驗證 ID 令牌。

   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 want to restrict access to only members of your G Suite domain, verify that the ID token has an hd claim that matches your G Suite domain name.

   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.

   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 want to restrict access to only members of your G Suite domain, also verify the hd claim by checking the domain name returned by the Payload.getHostedDomain() method.

   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(CLIENT_ID);
   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 request specified a G Suite 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 want to restrict access to only members of your G Suite domain, also verify the hd claim matches your G Suite domain name.

   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 = $payload['sub'];
     // If request specified a G Suite domain:
     //$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 want to restrict access to only members of your G Suite domain, also verify the hd claim matches your G Suite domain name.

   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 auth request is from a G Suite domain:
       # if idinfo['hd'] != GSUITE_DOMAIN_NAME:
       #     raise ValueError('Wrong hosted domain.')
   
       # 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.

   要點：令牌在返回的ID credential場，而不是g_csrf_token領域。

3. 根據 ID 令牌中電子郵件地址的關聯帳戶狀態，您可以將用戶重定向到不同的流，如下所示：

   • 未註冊的電子郵件地址：您可以顯示的註冊用戶界面（UI），它允許用戶提供其他資料信息，如果需要的話。它還允許用戶以靜默方式創建新帳戶和登錄用戶會話。

   • 存在的電子郵件地址舊版帳戶：您可以顯示一個網頁，允許最終用戶輸入自己的密碼，並與他們的谷歌憑證鏈接舊帳戶。這確認用戶有權訪問現有帳戶。

   • 一個returning聯盟的用戶：您可以默默登錄用戶。