title: What is the proper HTTP response to send for requests that require SSL/TLS
body: <p>I'm designing an RESTful API where some calls are public over HTTP, and some require an API key and encryption over HTTPS.  I'm deliberating on what response code should be sent if an HTTP request is sent to one of the private resources.  So far the only one that jumps out at me is <strong>412 - Precondition Failed</strong>, but the standard indicates that the precondition is imposed by the requester not the server.</p>
  
  <p>Is there an appropriate response code for this condition or do I just need to give in and do <strong>400</strong>?</p>