AJ #Level 20 End Day You don't... or at least you shouldn't. RESTful services should never maintain session information on any server. The very nature of RESTful services is to allow each client call to run in isolation from any previous call. Access to a resource should be self contained within the individual request.
Try searching on RESTful statelessness. That might provide more links on this architecture.
Here is a link that might give you additional context.
NOTE: Scroll down to the section titled:
NOTE: There are several good answers in this thread.