With T102566 a bunch of wikis will have InstantCommons broken, and will probably try to find out from the error logs what's wrong. MWHttpRequest does not seem to do any error logging whatsoever, though.
There are two cases that users will encounter due to T102566 and where we should provide a helpful error message:
- MWHttpRequest refuses to follow a HTTP->HTTPS redirect
- MWHttpRequest cannot verify the Wikimedia cert (note that while Commons has been reverted to HTTPS, upload.wikimedia.org has not, so this is happening right now)
Note that this does not affect InstantCommons which does not use MWHttpRequest directly.