Only set host header if it's sent before.

server.js

@@ -111,7 +111,9 @@ function processRequest(req, res)
 		}
 
         // Make sure the host header is to the URL we're requesting, not thingproxy
-        req.headers["host"] = remoteURL.host;
+        if(req.headers["host"]) {
+            req.headers["host"] = remoteURL.host;
+        }
 
 		var proxyRequest = request({
 			url: remoteURL,