Questa pagina è stata tradotta dall'API Cloud Translation.

Autenticarsi con un server di backend

Se utilizzi Accedi con Google su un'app o un sito che comunica con un server di backend, potresti dover identificare l'utente che attualmente ha eseguito l'accesso al server. Per farlo in modo sicuro, dopo che un utente ha eseguito correttamente l'accesso, invia il token ID dell'utente al tuo server tramite HTTPS. Quindi, sul server, verifica l'integrità del token ID e utilizza le informazioni utente contenute nel token per stabilire una sessione o creare un nuovo account.

Avviso: non accettare semplici ID utente, come quelli che puoi ricevere con GIDGoogleUser.userID property, sul tuo server di backend. Un'applicazione client modificata può inviare ID utente arbitrari al server per impersonare gli utenti, quindi devi utilizzare token ID verificabili per ottenere in modo sicuro gli ID utente degli utenti che hanno eseguito l'accesso sul lato server.

Invia il token ID al tuo server

Dopo che un utente ha eseguito correttamente l'accesso, recupera il token ID dell'utente:

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).
      }];
}];

Quindi, invia il token ID al tuo server con una richiesta POST HTTPS:

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);
                         }
                       }];

Verificare l'integrità del token ID

Dopo aver ricevuto il token ID tramite HTTPS POST, devi verificare l'integrità del 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.

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"
}

Warning: Once you get these claims, you still need to check that the aud claim contains one of your app's client IDs. If it does, then the token is both valid and intended for your client, and you can safely retrieve and use the user's unique Google ID from the sub claim.

If you are a G Suite customer, you might also be interested in the hd claim, which indicates the hosted domain of the user. This can be used to restrict access to a resource to only members of certain domains. The absence of this claim indicates that the user does not belong to a G Suite hosted domain.

Crea un account o una sessione

Dopo aver verificato il token, controlla se l'utente è già incluso nel tuo database utenti. In questo caso, definisci una sessione autenticata per l'utente. Se l'utente non è ancora nel tuo database utente, crea un nuovo record utente utilizzando le informazioni nel payload del token ID e definisci una sessione per l'utente. Puoi chiedere all'utente eventuali informazioni di profilo aggiuntive necessarie quando rileva un utente appena creato nella tua app.

Protezione degli account degli utenti con la Protezione su più account

Quando ti affidi a Google per l'accesso di un utente, potrai usufruire automaticamente di tutte le funzionalità di sicurezza e dell'infrastruttura create da Google per salvaguardare i dati dell'utente. Tuttavia, nel caso improbabile che l'Account Google dell'utente venga compromesso o che si verifichino altri eventi di sicurezza significativi, la tua app può anche essere vulnerabile ad attacchi. Per proteggere meglio i tuoi account da eventuali eventi di sicurezza importanti, utilizza la protezione su più account per ricevere avvisi di sicurezza da Google. Quando ricevi questi eventi, puoi vedere le modifiche importanti apportate alla sicurezza dell'Account Google dell'utente e intervenire sul servizio per proteggere i tuoi account.