It currently still works to POST to the API via http instead of https. But we'd really like to stop allowing that, see https://phabricator.wikimedia.org/T105794. Thus, the API will now return a warning if https was expected but not used.

If you run a bot, please check your configuration to make sure that you're using https rather than http. If you're using a distinctive user agent for your bot (which you all are, right?[1]), you can now check whether your bot is using http by going to https://www.mediawiki.org/wiki/Special:ApiFeatureUsage, entering your agent (or any useful prefix of it), and looking for "https-expected".

If for some reason your bot cannot support https, you really should upgrade it to make that happen.

[1]: https://meta.wikimedia.org/wiki/User-Agent_policy