With my limited knowledge of HTTPS I started wondering: How do proxy servers filter HTTPS websites? I mean adding a proxy server is essentially a MITM attack which is what HTTPS was explicitly supposed to prevent
The only way I can think of is to block the server by IP and port. However with things like SNI and wildcard certificates this means that you could block legitimate content (assume that a site that must be blocked shares an IP with a site that must be available in this situation).
What does it do then? You can't read the content of the connection since its encrypted; all you know is that someone is most likely sending an HTTPS request to some IP address.