Add abuse protection to the ROI calculator form

The calculator endpoint was open to anyone, and it has been collecting
spam submissions. Add a layered guard that runs before anything is
written to the DB or sent to the AI provider:

- Cloudflare Turnstile CAPTCHA, verified server-side (active when
  TURNSTILE_* keys are configured; fails closed if unverifiable)
- Honeypot field that only bots fill in
- Signed, single-use form token enforcing a 4s minimum fill time
- Per-IP rate limiting (5 per 10 min, 25 per 24h)

Layers 2-4 need no configuration and work on their own, so submissions
are throttled immediately; adding Turnstile keys upgrades it to a full
challenge. Blocked submissions now stop the flow client-side instead of
silently showing a result.

Also sets `trust proxy` for correct client IPs behind nginx, caps the
JSON body at 32kb, and fixes a latent ReferenceError in the
"AI not configured" branch that called saveCalcSubmission() before the
variables it closes over were declared.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

security.js

@@ -0,0 +1,220 @@
+/**
+ * HOA LedgerIQ — Form abuse protection
+ *
+ * Layered defence for public form endpoints (ROI calculator, lead capture):
+ *
+ *   1. Cloudflare Turnstile  — real CAPTCHA, active when TURNSTILE_* keys are set.
+ *   2. Honeypot field        — a hidden input humans never fill in.
+ *   3. Signed form token     — proves the form was actually loaded, and enforces a
+ *                              minimum fill time (bots submit instantly).
+ *   4. Per-IP rate limiting  — caps bursts and daily volume from one source.
+ *
+ * Layers 2–4 need no configuration and work on their own; adding Turnstile keys
+ * upgrades the protection to a full CAPTCHA challenge.
+ */
+
+'use strict';
+
+const crypto = require('crypto');
+
+// ── Config ───────────────────────────────────────────────
+const TURNSTILE_SITE_KEY = process.env.TURNSTILE_SITE_KEY   || '';
+const TURNSTILE_SECRET   = process.env.TURNSTILE_SECRET_KEY || '';
+const TURNSTILE_VERIFY_URL = 'https://challenges.cloudflare.com/turnstile/v0/siteverify';
+
+// If no explicit secret is configured, generate one per process. Tokens then stop
+// validating across restarts — harmless, the client just fetches a fresh one.
+const FORM_SECRET = process.env.FORM_TOKEN_SECRET || crypto.randomBytes(32).toString('hex');
+
+const MIN_FILL_MS      = 4 * 1000;             // faster than this is not a human
+const MAX_TOKEN_AGE_MS = 2 * 60 * 60 * 1000;   // tokens expire after 2 hours
+
+// Sliding-window caps per IP: short burst window + daily ceiling.
+const RATE_WINDOWS = [
+  { windowMs: 10 * 60 * 1000,      max: 5,  label: '10 minutes' },
+  { windowMs: 24 * 60 * 60 * 1000, max: 25, label: '24 hours'   },
+];
+
+const turnstileEnabled = Boolean(TURNSTILE_SITE_KEY && TURNSTILE_SECRET);
+
+// ── Signed, single-use form tokens ───────────────────────
+const usedTokens = new Map();   // token -> expiry ms
+const hits       = new Map();   // ip -> [timestamps]
+
+function sign(payload) {
+  return crypto.createHmac('sha256', FORM_SECRET).update(payload).digest('hex').slice(0, 32);
+}
+
+function issueFormToken() {
+  const payload = `${Date.now()}.${crypto.randomBytes(9).toString('base64url')}`;
+  return `${payload}.${sign(payload)}`;
+}
+
+function verifyFormToken(token) {
+  if (typeof token !== 'string' || token.length > 200) {
+    return { ok: false, reason: 'missing_token' };
+  }
+
+  const parts = token.split('.');
+  if (parts.length !== 3) return { ok: false, reason: 'bad_token' };
+
+  const [tsRaw, nonce, sig] = parts;
+  const expected = sign(`${tsRaw}.${nonce}`);
+  if (sig.length !== expected.length ||
+      !crypto.timingSafeEqual(Buffer.from(sig), Buffer.from(expected))) {
+    return { ok: false, reason: 'bad_token' };
+  }
+
+  const issuedAt = Number(tsRaw);
+  if (!Number.isFinite(issuedAt)) return { ok: false, reason: 'bad_token' };
+
+  const age = Date.now() - issuedAt;
+  if (age > MAX_TOKEN_AGE_MS || age < -60_000) return { ok: false, reason: 'expired_token' };
+  if (age < MIN_FILL_MS)                        return { ok: false, reason: 'too_fast' };
+  if (usedTokens.has(token))                    return { ok: false, reason: 'replayed_token' };
+
+  usedTokens.set(token, Date.now() + MAX_TOKEN_AGE_MS);
+  return { ok: true };
+}
+
+// ── Rate limiting ────────────────────────────────────────
+function clientIp(req) {
+  // Requires `app.set('trust proxy', ...)` when running behind nginx.
+  return req.ip || req.socket?.remoteAddress || 'unknown';
+}
+
+/** Check the caps without consuming a slot. */
+function checkRateLimit(ip) {
+  const now  = Date.now();
+  const list = hits.get(ip) || [];
+
+  for (const { windowMs, max, label } of RATE_WINDOWS) {
+    const recent = list.filter(t => now - t < windowMs).length;
+    if (recent >= max) return { ok: false, reason: 'rate_limited', label };
+  }
+  return { ok: true };
+}
+
+/** Record a successful submission against the caller's IP. */
+function recordSubmission(ip) {
+  const now    = Date.now();
+  const widest = Math.max(...RATE_WINDOWS.map(w => w.windowMs));
+  const list   = (hits.get(ip) || []).filter(t => now - t < widest);
+  list.push(now);
+  hits.set(ip, list);
+}
+
+// ── Turnstile ────────────────────────────────────────────
+async function verifyTurnstile(token, ip) {
+  if (!turnstileEnabled) return { ok: true, skipped: true };
+  if (typeof token !== 'string' || !token) return { ok: false, reason: 'captcha_missing' };
+
+  try {
+    const body = new URLSearchParams({ secret: TURNSTILE_SECRET, response: token });
+    if (ip && ip !== 'unknown') body.set('remoteip', ip);
+
+    const resp = await fetch(TURNSTILE_VERIFY_URL, {
+      method:  'POST',
+      headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+      body,
+      signal:  AbortSignal.timeout(8000),
+    });
+    const data = await resp.json();
+
+    if (!data.success) {
+      return { ok: false, reason: 'captcha_failed', codes: data['error-codes'] };
+    }
+    return { ok: true };
+  } catch (err) {
+    console.error('Turnstile verify error:', err.message);
+    // Fail closed: an unverifiable challenge is not a passed challenge.
+    return { ok: false, reason: 'captcha_unavailable' };
+  }
+}
+
+// ── Combined guard ───────────────────────────────────────
+const MESSAGES = {
+  honeypot:            'Submission rejected.',
+  missing_token:       'Your session expired. Please reload the page and try again.',
+  bad_token:           'Your session expired. Please reload the page and try again.',
+  expired_token:       'Your session expired. Please reload the page and try again.',
+  replayed_token:      'This form was already submitted. Please reload the page to run another estimate.',
+  too_fast:            'That was a little too quick — please take a moment and try again.',
+  rate_limited:        'Too many submissions from this network. Please try again later.',
+  captcha_missing:     'Please complete the verification challenge.',
+  captcha_failed:      'Verification failed. Please try the challenge again.',
+  captcha_unavailable: 'Verification is temporarily unavailable. Please try again in a moment.',
+};
+
+const STATUS = { rate_limited: 429, honeypot: 400 };
+
+/**
+ * Run every protection layer for a public form POST.
+ * Returns { ok: true, ip } or { ok: false, status, error, reason }.
+ */
+async function guardSubmission(req, { honeypotField = 'hp_company_url' } = {}) {
+  const ip   = clientIp(req);
+  const body = req.body ?? {};
+
+  const fail = ({ reason, label }) => ({
+    ok:     false,
+    reason,
+    status: STATUS[reason] ?? 403,
+    error:  label ? `${MESSAGES[reason]} (limit: ${label})` : MESSAGES[reason],
+  });
+
+  // 1. Honeypot — any value at all means a bot filled every field it found.
+  if (typeof body[honeypotField] === 'string' && body[honeypotField].trim() !== '') {
+    console.warn(`[abuse] honeypot tripped from ${ip}`);
+    return fail({ reason: 'honeypot' });
+  }
+
+  // 2. Rate limit (checked before the outbound Turnstile call).
+  const rate = checkRateLimit(ip);
+  if (!rate.ok) {
+    console.warn(`[abuse] rate limit hit by ${ip}`);
+    return fail(rate);
+  }
+
+  // 3. Signed single-use token + minimum fill time.
+  const tok = verifyFormToken(body.formToken);
+  if (!tok.ok) {
+    console.warn(`[abuse] form token rejected (${tok.reason}) from ${ip}`);
+    return fail(tok);
+  }
+
+  // 4. CAPTCHA.
+  const captcha = await verifyTurnstile(body.captchaToken, ip);
+  if (!captcha.ok) {
+    console.warn(`[abuse] captcha rejected (${captcha.reason}) from ${ip}`);
+    return fail(captcha);
+  }
+
+  recordSubmission(ip);
+  return { ok: true, ip };
+}
+
+function publicConfig() {
+  return { turnstileSiteKey: turnstileEnabled ? TURNSTILE_SITE_KEY : null };
+}
+
+// ── Housekeeping ─────────────────────────────────────────
+const sweep = setInterval(() => {
+  const now = Date.now();
+  for (const [token, exp] of usedTokens) if (exp < now) usedTokens.delete(token);
+
+  const widest = Math.max(...RATE_WINDOWS.map(w => w.windowMs));
+  for (const [ip, list] of hits) {
+    const kept = list.filter(t => now - t < widest);
+    if (kept.length) hits.set(ip, kept); else hits.delete(ip);
+  }
+}, 10 * 60 * 1000);
+sweep.unref?.();
+
+module.exports = {
+  turnstileEnabled,
+  issueFormToken,
+  guardSubmission,
+  publicConfig,
+  clientIp,
+};