Issuer REST Jira API Auth with JWT

I am testing the REST JIRA API and I wonder where I could get the iss to use it in my claims as it seems as the only thing that puts a barrier to login a user.

I’ll use node.js.

It mentions a clientKey

I’ll be using this package:

I have looked up clientKey and it talks about the OAuth, is this the case?

Jira is hosted on Cloud

I’ve also seen this

What kind of authentication I need to send api request on the cloud server?
I am making an app that uses the api to create, edit, ecc…