logout method
logout clears your apps local session and refresh tokens. You will
no longer be able to make requests to fetch the SnapchatUser
with
currentUser.
Call closeStream to close the stream and prevent a resource sink.
Implementation
Future<void> logout() async {
await _channel.invokeMethod('callLogout');
this._authStatusController.add(null);
this._authStateListener?.onLogout();
}