After implementing Authentication in your app, you can check if a user is logged in. `CognitoAuthSession` will have the `isSignedIn` property set to `false` if the user has not signed in to your app. You can see how it works by using the below function:

```dart
Future<bool> isUserSignedIn() async {
  final result = await Amplify.Auth.fetchAuthSession();
  return result.isSignedIn;
}
```

In case you want to get the current user information, you can use the code below:

```dart
Future<AuthUser> getCurrentUser() async {
  final user = await Amplify.Auth.getCurrentUser();
  return user;
}
```

`AuthUser` will have the `userId` and `username` will have the user details if they were logged in.