If you make a typo on the protocol, you get this error message:
taavi@runko:~/src/mediawiki master $ curl --request POST http://en.wikipedia.org/ <html><body><h1>403 Forbidden</h1> Request forbidden by administrative rules. </body></html>
Request forbidden by administrative rules. is confusing and does not provide any useful information for troubleshooting.
I think this changed when moving the port 80 listener to HAProxy. On deployment-prep (which is on the old system) you get our standard error page with this much more helpful error message:
Error: 403, Insecure Request Forbidden - use HTTPS - https://lists.wikimedia.org/pipermail/mediawiki-api-announce/2016-May/000110.html