I recently needed to monitor the HTTP traffic of an application that I wrote in order to debug why things were failing. Unfortunately, a simple proxy wouldn't work since the HTTPS traffic is encryped by SSL. This makes sense, since you really would hope that the data you send when surfing on a secure web page would be secure. I ended up solving this problem the same way you can solve every programming problem in the world: add a layer of indirection.
To start, I downloaded and installed the latest binaries of stunnel. Before starting, I modified the conf file to add the following entry:
Then, I installed tcpTrace and set things up to Listen on port 8079 and forward to localhost:8080. Lastly, in my application, I connected to http://localhost:8079/MyPath. This would eventually forward all of the traffic to the real destination, but I was able to spy on the details in tcpTrace since that was just HTTP traffic.
After doing this, I could see where things were malformed and clean my code up to submit things in the desired format.