# google_identity_services_web

A JS-interop layer for Google Identity's Sign In With Google SDK.

See the original JS SDK reference:

* [Sign In With Google](https://developers.google.com/identity/gsi/web)

## Usage

This package is the Dart JS-interop layer of the new **Sign In With Google**
SDK. Here's the API references for both of the sub-libraries:

* `id.dart`: [Sign In With Google JavaScript API reference](https://developers.google.com/identity/gsi/web/reference/js-reference)
* `oauth2.dart`: [Google 3P Authorization JavaScript Library for websites - API reference](https://developers.google.com/identity/oauth2/web/reference/js-reference)
* `loader.dart`: An (optional) loader mechanism that installs the library and
resolves a `Future<void>` when it's ready.

### Loading the SDK

There are two ways to load the JS SDK in your app.

#### Modify your index.html (most performant)

The most performant way is to modify your `web/index.html` file to insert a
script tag [as recommended](https://developers.google.com/identity/gsi/web/guides/client-library).
Place the `script` tag in the `<head>` of your site:

<?code-excerpt "example/web/index-with-script-tag.html (script-tag)"?>
```html
<head>
<!-- ··· -->
  <!-- Include the GSI SDK below -->
  <script src="https://accounts.google.com/gsi/client" async defer></script>
</head>
```

#### With the `loadWebSdk` function (on-demand)

An alternative way, that downloads the SDK on demand, is to use the
**`loadWebSdk`** function provided by the library. A simple location to embed
this in a Flutter Web only app can be the `main.dart`:

<?code-excerpt "example/lib/main.dart (use-loader)"?>
```dart
import 'package:google_identity_services_web/loader.dart' as gis;
// ···
void main() async {
  await gis.loadWebSdk(); // Load the GIS SDK
  // The rest of your code...
  // ···
}

```

(Note that the above won't compile for mobile apps, so if you're developing a
cross-platform app, you'll probably need to hide the call to `loadWebSdk`
behind a [conditional import/export](https://dart.dev/guides/libraries/create-library-packages#conditionally-importing-and-exporting-library-files).)

### Using the SDK

Once the SDK has been loaded, it can be used by importing the correct library:

* `import 'package:google_identity_services/id.dart';` for Authentication.
  * This will expose an `id` JSObject that binds to `google.accounts.id`.
* `import 'package:google_identity_services/oauth2.dart';` for Authorization.
  * This will expose an `oauth2` JSObject that binds to `google.accounts.oauth2`.

### Troubleshooting

Watch the browser's development tools JS console while using this package.
Information about errors during initialization and use of the library will be
displayed there.

Some common issues identified so far:

#### The given origin is not allowed for the given client ID

> When you perform local tests or development, **you must add both**
> `http://localhost` and `http://localhost:<port_number>` to the
> **Authorized JavaScript origins** box.
> The [Referrer-Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Referrer-Policy)
> response header must also be set to `no-referrer-when-downgrade` when using
> http and localhost.

* Read more: [Sign In with Google for Web - Setup - Get your Google API client ID](https://developers.google.com/identity/gsi/web/guides/get-google-api-clientid#get_your_google_api_client_id).

## Browser compatibility

The new SDK is introducing concepts that are on track for standardization to
most browsers, and it might not be compatible with older browsers.

Refer to the official documentation site for the latest browser compatibility
information of the underlying JS SDK:

* **Sign In With Google > [Supported browsers and platforms](https://developers.google.com/identity/gsi/web/guides/supported-browsers)**
