A resource representing state information. May have additional
properties attached to it. To support stateful interface, the client
must attach StateInfo to every message it sends.
Otherwise a new session will be initiated.
Identifies state/session context. Range be a resource.
Asks the server to discard session information and to free
A reply stating that the state information was not passed,
but is required.
A reply stating that the state information passed
it invalid, outdated etc.