The One Tap sign-in client retrieves a Google ID token when the user selects aGoogle Account. An ID token is a signed assertion of a user's identity that alsocontains a user's basic profile information, possibly including an email addressthat has been verified by Google.
When ID tokens are available, you can use them to securely authenticate withyour app's backend, or to automatically sign up the user for a new accountwithout the need to verify the user's email address.
To sign in or sign up a user with an ID token, send the token to your app'sbackend. On the backend, verify the token using either a Google API clientlibrary or a general-purpose JWT library. If the user hasn't signed in to yourapp with this Google Account before, create a new account.
If you've optionally chosen to use a nonce to help avoid replay attacks, usegetNonceto send it along with the ID Token to your backend server, and check for theexpected value. We recommend that you strongly consider using a nonce toimprove user safety and security.
Get an ID token from the credentials object
After you retrieve a user's credentials, check if the credentials objectincludes an ID token. If it does, send it to your backend.
Java
public class YourActivity extends AppCompatActivity { // ... private static final int REQ_ONE_TAP = 2; // Can be any integer unique to the Activity. private boolean showOneTapUI = true; // ... @Override protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) { super.onActivityResult(requestCode, resultCode, data); switch (requestCode) { case REQ_ONE_TAP: try { SignInCredential credential = oneTapClient.getSignInCredentialFromIntent(data); String idToken = credential.getGoogleIdToken(); if (idToken != null) { // Got an ID token from Google. Use it to authenticate // with your backend. Log.d(TAG, "Got ID token."); } } catch (ApiException e) { // ... } break; } }}Kotlin
class YourActivity : AppCompatActivity() { // ... private val REQ_ONE_TAP = 2 // Can be any integer unique to the Activity private var showOneTapUI = true // ... override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) { super.onActivityResult(requestCode, resultCode, data) when (requestCode) { REQ_ONE_TAP -> { try { val credential = oneTapClient.getSignInCredentialFromIntent(data) val idToken = credential.googleIdToken when { idToken != null -> { // Got an ID token from Google. Use it to authenticate // with your backend. Log.d(TAG, "Got ID token.") } else -> { // Shouldn't happen. Log.d(TAG, "No ID token!") } } } catch (e: ApiException) { // ... } } } // ...}Verify the integrity of the ID token
After you receive the ID token by HTTPS POST, you must verify the integrity of the 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-Controlheader in the response to determine when you should retrieve them again. - The value of
audin 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
issin the ID token is equal toaccounts.google.comorhttps://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
hdclaim, 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.
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.
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.
To validate an ID token in Node.js, use the Google Auth Library for Node.js. Install the library:
npm install google-auth-library --saveThen, 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 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 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.
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/apiclientThen, 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 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.
To validate an ID token in Python, use the verify_oauth2_token function. For example:
from google.oauth2 import id_tokenfrom 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.
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": "[email protected]", "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"} 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.
Create an account or session
After you have verified the token, check if the user is already in your user database. If so, establish an authenticated session for the user. If the user isn't yet in your user database, create a new user record from the information in the ID token payload, and establish a session for the user. You can prompt the user for any additional profile information you require when you detect a newly created user in your app.
Securing your users' accounts with Cross Account Protection
When you rely on Google to sign in a user, you'll automatically benefit from all of the security features and infrastructure Google has built to safeguard the user's data. However, in the unlikely event that the user's Google Account gets compromised or there is some other significant security event, your app can also be vulnerable to attack. To better protect your accounts from any major security events, use Cross Account Protection to receive security alerts from Google. When you receive these events, you gain visibility into important changes to the security of the user's Google account and you can then take action on your service to secure your accounts.
