Scalar uses a registration key to restrict open registrations. This issue arose in 2017 when developers discovered a bug that allowed anyone to register for a public-facing scalar.usc.edu/works installation. When the key is generated, the user must add it to the user registration form during account sign-up.
Reclaim Hosting’s installer for Scalar does not create this key; instead, it can be a key that you create. During the installation process, there is a field where you can add a custom code of your choice, to restrict user registration.
If you need to manage the key, you can add it to your local-settings.php file. Scalar has that documented here: Managing a custom Scalar install with local_settings.php
You can read more about the Registration Key here: http://scalar.usc.edu/works/guide2/restricting-registrations