Real life usage of the X-Forwarded-Host header?

Question

I\'ve found some interesting reading on the X-Forwarded-* headers, including the Reverse Proxy Request Headers section in the Apache documentation, as well as the

Answer 1

One example could be a proxy that blocks certain hosts and redirects them to an external block page. In fact, I’m almost certain my school filter does this…

(And the reason they might not just pass on the original Host as Host is because some servers [Nginx?] reject any traffic to the wrong Host.)