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Verify the Google ID token on your server side

After Google returns an ID token, it's submitted by an HTTP POST method request, with the parameter name credential, to your login endpoint.

The following is an example in the Python language that shows the usual steps to validate and consume the ID token:

  1. Verify the Cross-Site Request Forgery (CSRF) token. When you submit credentials to your login endpoint, we use the double-submit-cookie pattern to prevent CSRF attacks. Before each submission, we generate a token. Then, the token is put into both the cookie and the post body, as shown in the following code example:

    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. Verify the ID token.

    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.

  3. Based on the correlated account status for the email address in the ID token, you can redirect the user to different flows, as follows:

    • An unregistered email address: You can show a sign-up user interface (UI) that allows the user to provide additional profile information, if required. It also allows the user to silently create the new account and a logged-in user session.

    • A legacy account that exists for the email address: You can show a web page that allows the end user to input their password and link the legacy account with their Google credentials. This confirms that the user has access to the existing account.

    • A returning federated user: You can silently sign the user in.