In my previous post "REST and Workflow services play well together", I mentioned that Http Cookies were one of the built-in mechanisms for transferring the workflow context across calls between the client and the service. While cookies work well for http services, from my point of view, simple Http Headers naturally fit better in a REST architecture. As consequence, I decided to extend the WCF channel stack to support a new a custom channel (Or custom binding) for transferring the workflow context as a http header.
REST is not just about CRUD interfaces for your services, a complete long-running workflow can be modeled through the basic verbs as well. As my friend Jesus mentioned, the article "How to get a cup of coffee" represents an excellent source about this topic.
According to the Http specification, any Http GET request should be idempotent and safe. In this context, these principles have the following meaning: