[Twisted-Python] What is the right way to pass variables from Site to Resource?

I've got some global state and configuration information. It seems to me that they ought to be members of my Site, but I don't see any obvious way in a Resource.render_* to get the current Site. Neither Request nor Resource have a instance or method that returns its Site that I can find. Am I missing something, or am I confused about the Twisted way of doing things?