sannag:

Since 400 is a "Bad Request" according to Wikipedia, I'd expect that your URL isn't correct or a similar problem.

You might try visiting the site with Chrome and using the Developer tools panel to capture an actual interaction with the site and compare it with the values you're trying to use in your code.

Update: I just notice that your code is saying that you'll be posting form-encoded data, then you encode a JSON document, and don't include it in the POST. I think you're skipping a step or two...

...roboticus

When your only tool is a hammer, all problems look like your thumb.