неплохо вкостылено > Another way to learn about an onion site is if the website administrator has implemented a feature called Onion-Location. Onion-Location is a non-standard HTTP header that websites can use to advertise their onion counterpart. If the website that you are visiting has an onion site available, a purple suggestion pill will prompt at the URL bar in Tor Browser displaying ".onion available". When you click on ".onion available", the website will be reloaded and redirected to its onion counterpart.

Что нажать чтобы HTTP-сервер с поддержкой RFC6091?

Подскажите лёгкий httpd, способный рисовать разумные диролистинги, с TLS через gnutls.