How to lock unauthorized access on jira server

[Bhagya Roy]

We have a Jira board for service request 

here a random person is able to signup using his email , normally jira server should be enabled signup for there on own staff of your own companies not for pulica because attacker can see your running project

Ideally, a customer would not be able to sign up at the portal, but if a support person were to CC a customer we’d want external folks to be able to get email updates from the project.

Is there any possible way to lock this feature?