This is a proof of concept, enabling HAProxy to use _either_ SNI to redirect to backends with their own HTTPS certificates (which are then fully exposed to the client; HAProxy only proxies on a TCP level in that case), _as well as_ to terminate HTTPS and use the Host header to redirect to backends that use HTTP (or a new HTTPS connection).
1. The `http_redirect_frontend` is only there to listen on port 80 and redirect every request to HTTPS.
2. The `https_sni_frontend` listens on port 443 and chooses a backend based on the SNI hostname of the TLS connection.
3. The `https_termination_backend` passes all requests to a unix socket (using the plain TCP data).
4. The `https_termination_frontend` listens on said unix socket, terminates the HTTPS connections and then chooses a backend based on the Host header.
In the example (see [haproxy.cfg](haproxy.cfg)), the `pages_backend` is listening via HTTPS and is providing its own HTTPS certificates, while the `gitea_backend` only provides HTTP.
