getRequestHost returns comma separated list of hosts in some proxy setups

[Ingramz]

Environment

N/A

Reproduction

1. Set up multiple proxies such that Apache HTTP Server is within a chain, for instance the very last proxy before h3:
   User Agent -> Proxy (any, proxy1.tld) -> Apache httpd (proxy2.tld) -> h3

2. in h3 app, use getRequestHost({ xForwardedHost: true })

3. Returns proxy1.tld, proxy2.tld

Describe the bug

Some proxies (eg. Apache HTTP Server) append additional hosts to X-Forwarded-Host header when it is part of a multiple proxy chain.

This obscure behavior is thoroughly explained in RicoSuter/NSwag#2370. Due to the non standard nature of the X-Forwarded-Host header, there isn't any authoritative literature to link to, but Envoy proxy documentation corroborates that the hosts should be appended.

In such cases only the first host similarly to X-Forwarded-For header should be returned by the getRequestHost function instead.

Additional context

No response

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