security(relay): harden internet-facing relay server

Closes the account-takeover chain and related issues found in audit:

- WS auth brute-force protection: per-session lockout (authThrottle) + per-
  socket failure cap that closes the socket (1008); applied to both web-client
  and desktop auth. Failed auth no longer leaves the socket open for unlimited
  guesses.
- WS upgrades now pass an IP-based rate limiter and Origin allowlist before
  handleUpgrade (previously bypassed all HTTP middleware); trust proxy set so
  limiting keys on the real client IP.
- /health no longer leaks live session IDs (counts only).
- .env.example rate-limit fixed (900000ms / 300) from the accidental ~11k rps.
- Credentials moved out of URLs into the X-MacroPad-Password header; images
  fetched via header + blob URLs; login stores creds in sessionStorage.
- Session creation bounded (max sessions, min password length) and TTL-pruned;
  session store writes are now atomic (temp+rename) and debounced.
- Session IDs lengthened to 12 chars with rejection sampling (no modulo bias).
- Enable helmet CSP; restrict CORS to configured origins.
- Request IDs use crypto.randomUUID; drop postinstall build hook and uuid dep.
- Uniform response for unknown session IDs (removes enumeration oracle).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

macropad-relay/src/config.ts

@@ -5,6 +5,14 @@ import path from 'path';
 
 dotenv.config();
 
+function parseTrustProxy(): boolean | number | string {
+  const v = process.env.TRUST_PROXY ?? '1';
+  if (v === 'false') return false;
+  if (v === 'true') return true;
+  const n = Number(v);
+  return Number.isNaN(n) ? v : n;
+}
+
 export const config = {
   port: parseInt(process.env.PORT || '3000', 10),
   host: process.env.HOST || '0.0.0.0',
@@ -13,19 +21,47 @@ export const config = {
   dataDir: process.env.DATA_DIR || path.join(__dirname, '..', 'data'),
 
   // Session settings
-  sessionIdLength: parseInt(process.env.SESSION_ID_LENGTH || '6', 10),
+  sessionIdLength: parseInt(process.env.SESSION_ID_LENGTH || '12', 10),
+
+  // Maximum number of sessions that may exist at once
+  maxSessions: parseInt(process.env.MAX_SESSIONS || '1000', 10),
+
+  // Minimum password length enforced when creating a new session
+  minPasswordLength: parseInt(process.env.MIN_PASSWORD_LENGTH || '6', 10),
+
+  // Sessions unused for this many days are pruned
+  sessionTtlDays: parseInt(process.env.SESSION_TTL_DAYS || '90', 10),
 
   // Security
   bcryptRounds: parseInt(process.env.BCRYPT_ROUNDS || '10', 10),
 
-  // Rate limiting
+  // Rate limiting (HTTP)
   rateLimitWindowMs: parseInt(process.env.RATE_LIMIT_WINDOW_MS || '900000', 10), // 15 minutes
-  rateLimitMax: parseInt(process.env.RATE_LIMIT_MAX || '100', 10),
+  rateLimitMax: parseInt(process.env.RATE_LIMIT_MAX || '300', 10),
+
+  // WebSocket upgrade rate limiting (per IP)
+  wsUpgradeWindowMs: parseInt(process.env.WS_UPGRADE_WINDOW_MS || '60000', 10), // 1 minute
+  wsUpgradeMax: parseInt(process.env.WS_UPGRADE_MAX || '60', 10), // max upgrades per IP per window
+
+  // Auth brute-force protection
+  authMaxSocketFailures: parseInt(process.env.AUTH_MAX_SOCKET_FAILURES || '5', 10),
+  authLockoutMaxAttempts: parseInt(process.env.AUTH_LOCKOUT_MAX_ATTEMPTS || '10', 10),
+  authLockoutWindowMs: parseInt(process.env.AUTH_LOCKOUT_WINDOW_MS || '900000', 10), // 15 minutes
+  authLockoutDurationMs: parseInt(process.env.AUTH_LOCKOUT_DURATION_MS || '900000', 10), // 15 minutes
 
   // WebSocket
   pingInterval: parseInt(process.env.PING_INTERVAL || '30000', 10), // 30 seconds
   requestTimeout: parseInt(process.env.REQUEST_TIMEOUT || '30000', 10), // 30 seconds
 
+  // Origin / CORS allowlist (comma-separated). Empty = same-host only.
+  allowedOrigins: (process.env.ALLOWED_ORIGINS || '')
+    .split(',')
+    .map((o) => o.trim())
+    .filter((o) => o.length > 0),
+
+  // Trust the X-Forwarded-* headers from a reverse proxy
+  trustProxy: parseTrustProxy(),
+
   // Logging
   logLevel: process.env.LOG_LEVEL || 'info',