[bug-diffutils] bug#56468: [gnu.org #1853606] Re: bug#56468: www.gnu.org doesn't change http: to https:

[Paul Eggert]

On 7/28/22 15:16, Ian Kelling via RT wrote:

> If you
> can figure out a good test on the user agent string, please
> let us know.

Another possibility is to have the HTTP page load a script from HTTPS, 
and if that loads and runs correctly, have the script redirect to HTTPS. 
Or the script could do a more-elaborate test, such as checking whether 
the browser supports SNI. This should work for the use case prompting 
the bug report (a casual user on a modern browser), while not affecting 
ancient browsers, curl, etc. And it'd mean you wouldn't need to worry 
about maintaining a test based on user agent strings.

There's a 10-year-old serverfault post about doing this with SNI, here:

https://serverfault.com/questions/389806/redirect-to-ssl-only-if-browser-supports-sni

If you don't like the idea of a script, that post also talks about 
whitelisting user agents known to support SNI, whicch is more the sort 
of thing you're asking for.