Error code from the authorization server or SDK validation.
OptionalserverDescription: string
Optional error_description reported by the authorization
server. When present it is preferred over the canned message, because the
server description names the concrete cause (which audience was rejected,
which scope was refused) while the canned message only restates the code.
OptionalrawBody: unknown
Raw error body or underlying cause (optional)
Map authorization server error response to AnonymousSessionError. Populates description and cause fields from server response (CASCADE §D). Codes per DESIGN §3.C7.