Handling sessions
Any service accepts and returns an optional session object that can be passed to consecutive calls of the same or other services to possibly avoid authentication or authorization steps or at least speed things up.
While it might still work, a session object should be considered obsolete after passing it to a service.
Long-lived connection data
While sessions expire after a short amount of time and thus are not meant to get persisted, there is also the concept of long-lived connection data. In case credentials get persisted on the client for regular access, it is recommended to store and update connection data with them whenever a service returns some. Just like sessions, passing such data can avoid authentication and authorization steps and speed things up.