What is the proper HTTP response to send for requests that require SSL/TLS

http, httpresponse, https, rest, ssl

Solution

The most secure way to force HTTP client to use HTTPS is HTTP Strict Transport Security.

Previously a common suggestion was to drop the connection, but this practice has been removed in favor of HSTS (OWASP website).

Problem

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 412 - Precondition Failed, but the standard indicates that the precondition is imposed by the requester not the server. Is there an appropriate response code for this condition or do I just need to give in and do 400?

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