SessionModule provides access to Session object properties.
To get access to session properties use XPath syntax, e.g. to get the session
id use 'id' as the attribute name.
More complex expressions with functions are also supported, e.g.:
'substring(id, 8)'
will return the substring of id property of the session object.
NOTE: The module does not create a new session.
Returns the object which should be used as JXPath context.
Descendants should override this method to return a specific object
that is requried by the implementing class.
Examples are: request, session and application context objects.