A Flutter plugin for Google Sign In.

To use this plugin, follow the plugin installation instructions, then follow the platform integration steps below for all platforms you support.

• Android: Please see the google_sign_in_android README.
• iOS: Please see the google_sign_in_ios README.
• macOS: Please see the google_sign_in_ios README (which also supports macOS).
• Web: Please see the google_sign_in_web README.

Initialization and authentication #

Initialize the GoogleSignIn instance, and (optionally) start the lightweight authentication process:

final GoogleSignIn signIn = GoogleSignIn.instance;
unawaited(
  signIn.initialize(clientId: clientId, serverClientId: serverClientId).then((
    _,
  ) {
    signIn.authenticationEvents
        .listen(_handleAuthenticationEvent)
        .onError(_handleAuthenticationError);
    /// This example always uses the stream-based approach to determining
    /// which UI state to show, rather than using the future returned here,
    /// if any, to conditionally skip directly to the signed-in state.
    signIn.attemptLightweightAuthentication();
  }),
);

If the user isn't signed in by the lightweight method, you can show UI to start a sign-in flow. This uses authenticate on platforms that return true for supportsAuthenticate, otherwise applications should fall back to a platform-specific approach. For instance, user-initiated sign in on web must use a button rendered by the sign in SDK, rather than application-provided UI:

if (GoogleSignIn.instance.supportsAuthenticate())
  ElevatedButton(
    onPressed: () async {
      try {
        await GoogleSignIn.instance.authenticate();
      } catch (e) {
        // ···
      }
    },
    child: const Text('SIGN IN'),
  )
else ...<Widget>[
  if (kIsWeb)
    web.renderButton()
  // ···
],

If the user has previously authorized the scopes required by your application, you can silently request an access token for those scopes:

const List<String> scopes = <String>[
  'https://www.googleapis.com/auth/contacts.readonly',
];
    final GoogleSignInAccount? user = // ...
    final GoogleSignInClientAuthorization? authorization = await user
        ?.authorizationClient
        .authorizationForScopes(scopes);

Full list of available scopes.

If an app determines that the user hasn't granted the scopes it requires, it should initiate an Authorization request. On platforms where authorizationRequiresUserInteraction() returns true, this request must be initiated from a user interaction like a button press.

final GoogleSignInClientAuthorization authorization = await user
    .authorizationClient
    .authorizeScopes(scopes);

In the web, the accessToken is no longer refreshed. It expires after 3600 seconds (one hour), so your app needs to be able to handle failed REST requests, and update its UI to prompt the user for a new Authorization round.

This can be done by combining the error responses from your REST requests with the authorization methods described above.

For more details, take a look at the google_sign_in_web package.

If your application needs to access user data from a backend server, you can request a server auth code to send to the server:

final GoogleSignInServerAuthorization? serverAuth = await user
    .authorizationClient
    .authorizeServer(scopes);

Server auth codes are not always available on all platforms. For instance, on some platforms they may only be returned when a user initially signs in, and not for subsequent authentications via the lightweight process. If you need a server auth code you should request it as soon as possible after initial sign-in, and manage server tokens for that user entirely on the server side unless the signed in user changes.

On platforms where authorizationRequiresUserInteraction() returns true, this request must be initiated from a user interaction like a button press.

The Google Sign-In example application demonstrates one approach to using this package to sign a user in and authorize access to specific user data.

If you used version 6.x or earlier of google_sign_in, see the migration guide for more information about the changes.