syntax response if user is NOT logged in

[ssvw]

If a user is not logged in, the response should never be as follows (as it is now):

HTTP Status 400 - Bad Request
type Status report
message Bad Request
description The request sent by the client was syntactically incorrect.
Apache Tomcat/6.0.37

… even if the syntax of the posted serialization is indeed syntactically incorrect, but should instead be a "401 Unauthorized" error message.