If you use Google Sign-In with an app or site that communicates with a backend server, you might need to identify the currently signed-in user on the server. To do so securely, after a user successfully signs in, send the user's ID token to your server using HTTPS. Then, on the server, verify the integrity of the ID token and use the user information contained in the token to establish a session or create a new account.
Send the ID token to your server
After a user successfully signs in, get the user's ID token:
Swift
GIDSignIn . sharedInstance . signIn ( withPresenting : self ) { signInResult , error in guard error == nil else { return } guard let signInResult = signInResult else { return } signInResult . user . refreshTokensIfNeeded { user , error in guard error == nil else { return } guard let user = user else { return } let idToken = user . idToken // Send ID token to backend (example below). } }
Objective-C
[ GIDSignIn . sharedInstance signInWithPresentingViewController : self completion : ^ ( GIDSignInResult * _Nullable signInResult , NSError * _Nullable error ) { if ( error ) { return ; } if ( signInResult == nil ) { return ; } [ signInResult . user refreshTokensIfNeededWithCompletion :^ ( GIDGoogleUser * _Nullable user , NSError * _Nullable error ) { if ( error ) { return ; } if ( user == nil ) { return ; } NSString * idToken = user . idToken ; // Send ID token to backend (example below). }]; }];
Then, send the ID token to your server with an HTTPS POST request:
Swift
func tokenSignInExample ( idToken : String ) { guard let authData = try ? JSONEncoder (). encode ([ "idToken" : idToken ]) else { return } let url = URL ( string : "https://yourbackend.example.com/tokensignin" ) ! var request = URLRequest ( url : url ) request . httpMethod = "POST" request . setValue ( "application/json" , forHTTPHeaderField : "Content-Type" ) let task = URLSession . shared . uploadTask ( with : request , from : authData ) { data , response , error in // Handle response from your backend. } task . resume () }
Objective-C
NSString * signinEndpoint = @"https://yourbackend.example.com/tokensignin" ; NSDictionary * params = @{ @"idtoken" : idToken } ; NSMutableURLRequest * request = [ NSMutableURLRequest requestWithURL : signinEndpoint ]; [ request setValue : @"application/x-www-form-urlencoded" forHTTPHeaderField : @"Content-Type" ]; [ request setHTTPMethod : @"POST" ]; [ request setHTTPBody : [ self httpBodyForParamsDictionary : params ]]; NSOperationQueue * queue = [[ NSOperationQueue alloc ] init ]; [ NSURLConnection sendAsynchronousRequest : request queue : queue completionHandler : ^ ( NSURLResponse * response , NSData * data , NSError * error ) { if ( error ) { NSLog ( @"Error: %@" , error . localizedDescription ); } else { NSLog ( @"Signed in as %@" , data . bytes ); } }];
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.
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:
-
emailhas a@gmail.comsuffix, this is a Gmail account. -
email_verifiedis true andhdis 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.
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 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 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 --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 : 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 (); 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, 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/apiclient
verifyIdToken()
function. For example: 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 ) { $ 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, 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_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. 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": "testuser@gmail.com",
"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.
