Record private local signup request outcomes (#57)

infra/local/frontend/Caddyfile

@@ -5,6 +5,21 @@
 
 https://localhost:8443 {
 	tls internal
+	# Record signup status/timing even when the API rejects a request before
+	# account creation. Drop the entire request and response headers so URLs,
+	# cookies, addresses and browser-provided values cannot enter access logs.
+	log signup {
+		format filter {
+			wrap json
+			fields {
+				request delete
+				resp_headers delete
+				user_id delete
+			}
+		}
+	}
+	@otherRequests not path /api/v1/accounts/signup
+	log_skip @otherRequests
 	root * /srv
 	handle /api/* {
 		reverse_proxy bff:8082