The Session userId ties an active login to a specific User record. When a request arrives with a session token, piper resolves the userId to look up that user's SiteAccess grants and UserTenant role. This determines what actions the user may perform — Admin, Editor, or Viewer — across each site they have access to. Without a valid userId on an active session, all data access is denied.
Technical section
Data model, API, and internals — visible to developers.