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.

https://developer.atlassian.com/cloud/jira/platform/understanding-jwt/

It mentions a clientKey

I’ll be using this package:
https://bitbucket.org/atlassian/atlassian-jwt-js/src/master/

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

Jira is hosted on Cloud .atlassian.net

I’ve also seen this
https://developer.atlassian.com/cloud/jira/platform/rest/v3/#api-rest-api-3-applicationrole-key-get

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…