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:
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.')
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 toaccounts.google.com
orhttps://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
andhd
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 andhd
is set, this is a G Suite account.
Users may register for Google Accounts without using Gmail or G Suite. When
email
does not contain a@gmail.com
suffix andhd
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.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, theaud
claim, theiss
claim, and theexp
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 thePayload.getHostedDomain()
method. The domain of theemail
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:
Then, call thenpm install google-auth-library --save
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, theaud
claim, theexp
claim, and theiss
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):
Then, call thecomposer require google/apiclient
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, theaud
claim, theexp
claim, and theiss
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, theaud
claim, and theexp
claim. You must also verify thehd
claim (if applicable) by examining the object thatverify_oauth2_token
returns. If multiple clients access the backend server, also manually verify theaud
claim.- 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
Once the token's validity is confirmed, you can use the information in the Google ID token to correlate the account status of your site:
An unregistered user: 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.
An existing account that already exists in your site: 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.