# Users and Rollouts

To facilitate rollouts, and consistently serve the same value for a flag during a session, we need a way of identifying the user, which needs to be supplied by the application

```dart
@override
void initState() {
  initToggly();
  super.initState();
}

void initToggly() async {
  await Toggly.init(
    appKey: '<YOUR_APP_KEY>',
    environment: '<YOUR_APP_ENVIRONMENT>',
    userIdentifier: '<UNIQUE_USER_IDENTIFIER>',
  );
}
```

{% hint style="success" %}
When using user identifiers, evaluated features are cached per user for 30 minutes by default on a sliding window, so the user might not see the change right away as to not confuse the user. The session length is configurable and the session store can be cleared in **App Settings**
{% endhint %}


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