If you're using built-in authentication, you can block unauthenticated people from being able to create an account.

  1. In the upper-right corner of any page, click . Rocketship icon for accessing site admin settings

  2. In the left sidebar, click Management Console. Management Console tab in the left sidebar

  3. In the left sidebar, click Privacy. Privacy tab in the settings sidebar

  4. Unselect Enable sign-up. Enable sign-up checkbox

  5. Under the left sidebar, click Save settings. Save settings button