Scalar uses a registration key to restrict open registrations. This came about in 2017 when the developers discovered a bug that allows anyone to register for a public-facing scalar.usc.edu/works install. When the key is generated, the user is required to add it to the user registration form when signing up for an account.
Reclaim Hosting’s installer for Scalar does not create this key, rather this can be a key 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
