OAuth 2(3LO)

https://developer.atlassian.com/cloud/jira/platform/oauth-2-authorization-code-grants-3lo-for-apps/

https://developer.atlassian.com/apps/create

Build a app

You can build your own app locally and use it in Jira.

https://developer.atlassian.com/cloud/jira/platform/getting-started/

Go to http://go.atlassian.com/cloud-dev and register your instance.

Jira Projects are Jira Software. Jira Software is a Jira app.

Currently, I needn’t the build app feature.