I have a reverse proxy setup and I'm trying to 'link' access logs to upstream server events. What I've got so far is the following Caddy file:

localhost {
	reverse_proxy {
		to https://localhost:5000
		header_up X-Request-Id "{http.request.uuid}"
		transport http {
			tls
			tls_insecure_skip_verify
			read_buffer 8192
		}
	}
	log {
		level info
		# somehow include an additional field {..., requestId: "{http.request.uuid}"} in the log?
	}
}

The HTTP server at https://localhost:5000 can read the incoming X-Request-Id header just fine. But how can I write the same request ID to the access log to link them together (for deeper analysis in case of upstream server errors)?

Perhaps someone knows a work-around for this issue?