code: private static void assignKeyFromAddressNode(ModelNode payload, ModelNode address) {
          List<Property> props = address.asPropertyList();
          Property lastToken = props.get(props.size()-1);
          payload.get("entity.key").set(lastToken.getValue().asString());
      }
docs: the model representations we use internally carry along the entity keys.
  these are derived from the resource address, but will be available as synthetic resource attributes.
  
  @param payload
  @param address