Compare operator key in constant time

resolveIdentity and verifyOperatorKey compared the shared
relay_cloud_operator_key with ===/!==, which short-circuits on the first
differing byte — a timing oracle on a high-value key. Use a
timingSafeEqual-based constantTimeEqual, matching admin-auth.js.

server/identity.js

@@ -23,10 +23,25 @@
 // A route bills against `creditKey`; for tier it uses the stored row tier
 // (cloud) or `license.tier` (license) — see identityTier().
 
+import { timingSafeEqual } from "crypto";
 import { getConfigSnapshot } from "./config.js";
 import { resolveLicense } from "./keysat-client.js";
 import { getCreditKey } from "./credits.js";
 
+// Constant-time string compare for the shared operator key, so a token
+// guess can't be tuned byte-by-byte off response timing. Mirrors the
+// helper in admin-auth.js. A length mismatch returns false early —
+// length isn't the secret, and timingSafeEqual requires equal length.
+function constantTimeEqual(a, b) {
+  if (typeof a !== "string" || typeof b !== "string") return false;
+  if (a.length !== b.length) return false;
+  try {
+    return timingSafeEqual(Buffer.from(a), Buffer.from(b));
+  } catch {
+    return false;
+  }
+}
+
 // user-ids come from Recaps (base64url / hex account ids). Constrain the
 // charset so a header can't smuggle a path-ish or oversized key into the
 // ledger.
@@ -40,7 +55,7 @@ export async function resolveIdentity(req) {
     const cfg = await getConfigSnapshot();
     const expected = (cfg.relay_cloud_operator_key || "").trim();
     const presented = (req.header("X-Recap-Operator-Key") || "").trim();
-    if (!expected || !presented || presented !== expected) {
+    if (!expected || !presented || !constantTimeEqual(presented, expected)) {
       const e = new Error(
         "X-Recap-User-Id requires a valid X-Recap-Operator-Key"
       );
@@ -81,7 +96,7 @@ export async function verifyOperatorKey(req) {
   const cfg = await getConfigSnapshot();
   const expected = (cfg.relay_cloud_operator_key || "").trim();
   const presented = (req.header("X-Recap-Operator-Key") || "").trim();
-  return !!expected && !!presented && presented === expected;
+  return !!expected && !!presented && constantTimeEqual(presented, expected);
 }
 
 // The tier to bill/quota at for a resolved identity.