Mengautentikasi dengan server backend

Jika Anda menggunakan Login dengan Google dengan aplikasi atau situs yang berkomunikasi dengan server backend, Anda mungkin perlu mengidentifikasi pengguna yang saat ini sudah login di server. Untuk melakukannya dengan aman, setelah pengguna berhasil login, kirim token ID pengguna tersebut ke server Anda menggunakan HTTPS. Kemudian, pada server, verifikasi integritas token ID dan gunakan informasi pengguna yang terdapat dalam token untuk membuat sesi atau membuat akun baru.

Mengirim token ID ke server Anda

Pertama-tama, saat pengguna login, dapatkan token ID-nya:

1. Saat mengonfigurasi Login dengan Google, panggil metode requestIdToken dan teruskan client ID web server Anda.

   // Request only the user's ID token, which can be used to identify the
   // user securely to your backend. This will contain the user's basic
   // profile (name, profile picture URL, etc) so you should not need to
   // make an additional call to personalize your application.
   GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
           .requestIdToken(getString(R.string.server_client_id))
           .requestEmail()
           .build();

2. Saat aplikasi dimulai, periksa apakah pengguna sudah login ke aplikasi Anda menggunakan Google, di perangkat ini atau perangkat lain, dengan memanggil silentSignIn:

   GoogleSignIn.silentSignIn()
       .addOnCompleteListener(
           this,
           new OnCompleteListener<GoogleSignInAccount>() {
             @Override
             public void onComplete(@NonNull Task<GoogleSignInAccount> task) {
               handleSignInResult(task);
             }
           });

3. Jika pengguna tidak dapat login secara otomatis, tampilkan pengalaman logout seperti biasa, dengan memberi pengguna opsi untuk login. Saat pengguna login, dapatkan GoogleSignInAccount pengguna dalam hasil aktivitas intent login:

   // This task is always completed immediately, there is no need to attach an
   // asynchronous listener.
   Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
   handleSignInResult(task);

4. Setelah pengguna login secara otomatis atau eksplisit, dapatkan token ID dari objek GoogleSignInAccount:

   private void handleSignInResult(@NonNull Task<GoogleSignInAccount> completedTask) {
       try {
           GoogleSignInAccount account = completedTask.getResult(ApiException.class);
           String idToken = account.getIdToken();
   
           // TODO(developer): send ID Token to server and validate
   
           updateUI(account);
       } catch (ApiException e) {
           Log.w(TAG, "handleSignInResult:error", e);
           updateUI(null);
       }
   }

Kemudian, kirim token ID ke server Anda dengan permintaan POST HTTPS:

HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost("https://yourbackend.example.com/tokensignin");

try {
  List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
  nameValuePairs.add(new BasicNameValuePair("idToken", idToken));
  httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

  HttpResponse response = httpClient.execute(httpPost);
  int statusCode = response.getStatusLine().getStatusCode();
  final String responseBody = EntityUtils.toString(response.getEntity());
  Log.i(TAG, "Signed in as: " + responseBody);
} catch (ClientProtocolException e) {
  Log.e(TAG, "Error sending ID token to backend.", e);
} catch (IOException e) {
  Log.e(TAG, "Error sending ID token to backend.", e);
}

Memverifikasi integritas token ID

Setelah menerima token ID melalui HTTPS POST, Anda harus memverifikasi integritas 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 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 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:

• email has a @gmail.com suffix, this is a Gmail account.
• email_verified is true and hd 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 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.

Menggunakan Library Klien Google API

Menggunakan salah satu Library Klien Google API (mis. Java, Node.js, PHP, Python) adalah cara yang direkomendasikan untuk memvalidasi token ID Google di lingkungan produksi.

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.");
}

npm install google-auth-library --save

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);

composer require google/apiclient

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
}

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

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.

Membuat akun atau sesi

Setelah memverifikasi token, periksa apakah pengguna sudah ada di database pengguna Anda. Jika demikian, buat sesi yang diautentikasi untuk pengguna. Jika pengguna belum berada di database pengguna, buat record pengguna baru dari informasi dalam payload token ID, dan buat sesi untuk pengguna tersebut. Anda dapat meminta pengguna untuk memberikan informasi profil tambahan yang diperlukan saat mendeteksi pengguna yang baru dibuat di aplikasi Anda.

Mengamankan akun pengguna Anda dengan Perlindungan Lintas Akun

Jika Anda mengandalkan Google untuk memproses login pengguna, Anda akan otomatis mendapatkan manfaat dari semua fitur keamanan dan infrastruktur yang dibuat oleh Google untuk mengamankan data pengguna. Namun, seandainya Akun Google pengguna disusupi atau terjadi beberapa peristiwa keamanan signifikan lainnya, aplikasi Anda juga dapat rentan terhadap serangan. Untuk melindungi akun Anda dengan lebih baik dari peristiwa keamanan besar, gunakan Perlindungan Lintas Akun untuk menerima notifikasi keamanan dari Google. Saat menerima peristiwa ini, Anda dapat melihat perubahan penting pada keamanan Akun Google pengguna, dan Anda dapat mengambil tindakan pada layanan untuk mengamankan akun Anda.