This method can read the client protocol from the "X-Forwarded-Proto" header
when trusted proxies were set via "setTrustedProxies()".
The "X-Forwarded-Proto" header must contain the protocol: "https" or "http".
If your reverse proxy uses a different header name than "X-Forwarded-Proto"
("SSL_HTTPS" for instance), configure it via "setTrustedHeaderName()" with
the "client-proto" key.