Authenticates your organization using clientId and clientSecret. Returns a sessionId valid for 24 hours.

Optionally pass customerUid to scope the session to a specific user (sets deviceSessionType to User). Omit it for system-level operations (deviceSessionType: System).

The clientSecret is never sent again after this call. Store the returned sessionId and pass it on every subsequent request via the X-Session-Id header alongside X-Client-Id.