I am trying to make a HTTP Request to a JSON API like `https://api.github.com` using `tornado.httpclient` and I found that it always responses with FORBIDDEN 403. 

Simplifying, I make a request using the CLI with:

`$ python -m tornado.httpclient https://api.github.com`

getting a `tornado.httpclient.HTTPError: HTTP 403: Forbidden`.

In other hand, if I try to request this URL via browser or a simple `$ curl https://api.github.com`, the response is 200 OK and the proper JSON file.

What is causing this? Should I set some specific Headers on the `tornado.httpclient` request? What's the difference with a `curl` request?