Yes, if you aren’t using any other proxy (for example, Cloudflare) in front of Fly, then Fly-Client-IP would be the best header to use to identify the original requester. However, if there is any of these proxies in front, one would have to use X-Forwarded-For and parse the header as prescribed by MDN (because Fly-Client-IP will point to the proxy in this case, as we don’t know which proxies we are supposed to trust not to spoof the source IP when we parse X-Forwarded-For to set Fly-Client-IP).
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