The working directory the identity left, or null when it has none stored.
Stores the working directory for the identity.
The session's home: where it begins before it has a working directory of its own.
Who the session is, connected or not.
Prepares the backend's own state (configuration, stored credentials) before the session starts.
The session's user as the backend last knew them, or null when it knows none.
What a backend tells the core about the session it serves.