I have an HTTP serving an API which works either anonymously or with a secret key in a header, like so:
GET /profile?authenticationKey Authorization: 1234567890
I want to reject any request coming in over HTTP that uses an Authorization header, since those headers would come across in plain text. But I'm not sure what the appropriate response is.
I've considered 400 Bad Request with a note explaining why what they did was stupid and suggesting that they immediately invalidate their key.
But I'm wondering whether 426 Upgrade Required might be better or worse. It's a code specific to the idea that an HTTP request needs to be an HTTPS request, but reading RFC 2817 makes me think that it is designed to help switch to HTTPS from the same port. Can I use it in this case as well? If so, do I need to include an
Upgrade: TLS/1.0 header as well?