Fire up firefox and download the RESTClient Add-on.
Window -> Add-ons Manager
Search -> RESTClient
Method: 
  POST
URL: 
  http://ec2-184-73-40-56.compute-1.amazonaws.com/sessions.json
Headers: 
  Content-Type: application/json
Body:
  {
    "user": 
    {
      "email": "your@emailaddress.com", "password": "Your_Password"
    }
  }