It looks like each API request authenticated with basic auth returns a JSESSIONID cookie. However if that cookie is passed in the next API request instead of the basic auth credentials (i.e. to switch to using cookie authentication) then a 401 results.
If however I use the /auth/1/session API then the JSESSIONID cookie returned can be used successfully.
My goal is to avoid the extra round-trip to make the POST to /auth/1/session and instead use basic auth with the first API request and cookie authentication with subsequent requests (in order to meet the recommendation here https://jira.atlassian.com/browse/JRA-44654).
Does anyone know why the JSESSIONID from API requests can be used to authenticate the next request?