Log the client address next to the peer address (closes #270)

Behind a trusted proxy every log line named only the proxy, so abuse could not be traced from webhooker's own logs although the rate limiters already knew the client. The access log, the rate-limit rejection lines, the CSRF warning and the receiver's request line now carry clientIP next to remoteIP. remoteIP still means the connecting peer; clientIP is the address the rate limiters key on, the forwarded client when the peer is inside TRUSTED_PROXIES, worked out once per request by the same code. The README says the field is only as trustworthy as TRUSTED_PROXIES. The access log's 2,560-byte line ceiling holds with the field charged, and a size case with an oversized X-Forwarded-For pins it.

Model: opus-5-5

internal/middleware/csrf.go

@@ -45,10 +45,10 @@ func (m *Middleware) CSRF(
 		// unauthenticated client: a POST with no token to
 		// /hook/<any length of any text>/edit lands here. The
 		// method and path are capped against the same budgets as
-		// the access log. remote_addr is set by net/http from the
-		// accepted connection rather than by the client, and
+		// the access log. remoteIP and clientIP are the same
+		// addresses the access log carries, and
 		// csrf.FailureReason returns one of gorilla/csrf's own
-		// fixed error values, so neither is client-sized.
+		// fixed error values, so none of them is client-sized.
 		m.log.Warn("csrf: token validation failed",
 			"method", logfield.Truncate(
 				r.Method, maxLogMethodBytes,
@@ -56,7 +56,8 @@ func (m *Middleware) CSRF(
 			"path", logfield.Truncate(
 				r.URL.Path, logfield.MaxBytes,
 			),
-			"remote_addr", r.RemoteAddr,
+			"remoteIP", RemoteIP(r),
+			"clientIP", ClientIP(r),
 			"reason", csrf.FailureReason(r),
 		)
 		forbidden.ServeHTTP(w, r)