X-Forwarded-For carries a comma-separated list, and constructing a
QHostAddress from the raw header value returns a null address for it, so a
configured X-Forwarded-For or a multi-hop header never resolved and websocket
clients stayed on the proxy's address.
- Add parseForwardedAddress, returning the rightmost usable entry of a
forwarded header list
- Use it for the websocket handshake instead of parsing the raw value
- Exempt loopback from per-address auth rate limits so a same-host proxy with a
customized trusted_sources list cannot lock every user out
- Add forwarded_address_test
Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>
