The Portfolio API does not allow creation of person entities corresponding to existing Jira users. However, the persons are not guaranteed to exist for all Jira users. Please provide a way to create persons via the API.

It could be opening the gate on PersonAPI, but it could also ensure the person entity exists when creating a new resource.

There is a possible workaround with getting PersonService via ComponentAccessor and calling insertJiraUserIds on it, but it's pretty dirty as it's not part of the public API.