Use external HTTP Debugging tool. Your options include:
- node-http-proxy as seen in How do I use node.js http-proxy for logging HTTP traffic in a computer?
- middlefiddle written in node.js (but abandoned for 3 years now) https://github.com/mdp/middlefiddle
- mitmproxy – a CLI tool http://mitmproxy.org
- fiddler http://www.telerik.com/fiddler
- and many more – https://www.google.pl/search?q=HTTP+debugger
You fire up one of those, tell them where to route the traffic, and point your application at that debugging proxy instead of the real server.