add X-FORWARDED headers for proxy requests (#1677)

Author: johann-sonntagbauer

Diff for: packages/react-scripts/scripts/start.js

@@ -212,7 +212,8 @@ function addMiddleware(devServer) {
       onError: onProxyError(proxy),
       secure: false,
       changeOrigin: true,
-      ws: true
+      ws: true,
+      xfwd: true
     });
     devServer.use(mayProxy, hpm);