class ChromeIdentity extends ChromeApi {
 static final JsObject _identity = chrome['identity'];

 ChromeIdentity._();

 bool get available => _identity != null;

 /**
  * Gets an OAuth2 access token using the client ID and scopes specified in the
  * <a href="app_identity.html#update_manifest">`oauth2` section of
  * manifest.json</a>.
  * 
  * The Identity API caches access tokens in memory, so it's ok to call
  * `getAuthToken` any time a token is required. The token cache automatically
  * handles expiration.
  * 
  * [details]: Token options.
  * [callback]: Called with an OAuth2 access token as specified by the
  * manifest, or undefined if there was an error.
  */
 Future<String> getAuthToken([TokenDetails details]) {
   if (_identity == null) _throwNotAvailable();

   var completer = new ChromeCompleter<String>.oneArg();
   _identity.callMethod('getAuthToken', [jsify(details), completer.callback]);
   return completer.future;
 }

 /**
  * Removes an OAuth2 access token from the Identity API's token cache.
  * 
  * If an access token is discovered to be invalid, it should be passed to
  * removeCachedAuthToken to remove it from the cache. The app may then
  * retrieve a fresh token with `getAuthToken`.
  * 
  * [details]: Token information.
  * [callback]: Called when the token has been removed from the cache.
  */
 Future removeCachedAuthToken(InvalidTokenDetails details) {
   if (_identity == null) _throwNotAvailable();

   var completer = new ChromeCompleter.noArgs();
   _identity.callMethod('removeCachedAuthToken', [jsify(details), completer.callback]);
   return completer.future;
 }

 /**
  * Starts an auth flow at the specified URL.
  * 
  * This method enables auth flows with non-Google identity providers by
  * launching a web view and navigating it to the first URL in the provider's
  * auth flow. When the provider redirects to a URL matching the pattern
  * `https://&lt;app-id&gt;.chromiumapp.org/`, the window will close, and the
  * final redirect URL will be passed to the [callback] function.
  * 
  * [details]: WebAuth flow options.
  * [callback]: Called with the URL redirected back to your application.
  */
 Future<String> launchWebAuthFlow(WebAuthFlowDetails details) {
   if (_identity == null) _throwNotAvailable();

   var completer = new ChromeCompleter<String>.oneArg();
   _identity.callMethod('launchWebAuthFlow', [jsify(details), completer.callback]);
   return completer.future;
 }

 Stream<OnSignInChangedEvent> get onSignInChanged => _onSignInChanged.stream;

 final ChromeStreamController<OnSignInChangedEvent> _onSignInChanged =
     new ChromeStreamController<OnSignInChangedEvent>.twoArgs(_identity, 'onSignInChanged', _createOnSignInChangedEvent);

 void _throwNotAvailable() {
   throw new UnsupportedError("'chrome.identity' is not available");
 }
}