Reads an already-loaded session's conversation ExternalID (the anonymous scope id) under contextUser;
null when there is no conversation or it cannot be read (logged). For callers that loaded the session
through another gate and only need the scope half of AuthorizeSessionAccess's subject.
Reads an already-loaded session's conversation
ExternalID(the anonymous scope id) undercontextUser; null when there is no conversation or it cannot be read (logged). For callers that loaded the session through another gate and only need the scope half of AuthorizeSessionAccess's subject.