Our problem with HTTPS and user-created content
We have a departmental web server, where people can host their personal pages (eg) and pages for their research groups and so on, including user-run web servers behind reverse proxies. In other words, this web server has a lot of content, created by a lot of people, and essentially none of it is under our control. These days, in one sense this presents us with a bit of a problem.
Our departmental web server supports HTTPS (and has for years). Recent browser developments are clearly pushing websites from HTTP to HTTPS, even if perhaps not as much as has been heralded, and so it would be good if we were to actively switch over. But, well, there's an obvious problem for us, and the name of that problem is mixed content. A not insignificant number of pages on our web server refer to resources like CSS stylesheets using explicit HTTP URLs (either local ones or external ones), and so would and do break if loaded over HTTPS, where browsers generally block mixed content.
We are obviously not going to break user web pages just because the Internet would now kind of like to see us using HTTPS instead of HTTP; if we even proposed doing that, the users would get very angry at us. Nor is it feasible to get users to audit and change all of their pages to eliminate mixed content problems (and from the perspectives of many users, it would be make-work). The somewhat unfortunate conclusion is that we will never be able to do a general HTTP to HTTPS upgrade on our departmental web server, including things like setting HSTS. Some of the web server's content will always be in the long tail of content that will never migrate to HTTPS and will continue to be HTTP content for years to come.
Probably this issue is confronting anyone with significant amounts of user-created content, especially in situations where people wrote raw HTML, CSS, and so on. I suspect that a lot of these sites will stay HTTPS-optional for plenty of time to come.
(Our users can use a
.htaccess to force HTTP to HTTPS redirection
for their own content, although I don't expect very many people to
ever do that. I have set this up for my pages, partly just to make sure that
it worked properly, but I'm not exactly a typical person here.)