How do I get the LoggedInUser() in a service?

Jira Development Jira Data Center
1

I have a service extending from AbstractService and I tried to use

ComponentAssessor.getJiraAuthenticationContext().getLoggedInUser() but it returned null.

The service is run from a scheduler cron job

is there a way for me to get the User?

2

A service has no logged in user. It is correctly returning null.