InstantAdPay site skeleton: SIWE auth, live chain ledger, join links, buy flow

Zero-dependency Node server on the RM Circle pattern. Chain config lives in
the volume so the same code runs the Amoy dress rehearsal and mainnet.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

auth.js

@@ -0,0 +1,120 @@
+// Wallet sign-in (SIWE / EIP-4361) for InstantAdPay.
+// Pattern lifted from the RM Circle messages.js implementation (proven with
+// MetaMask's friendly sign-in UI). One free signature, cannot move funds.
+//
+// Difference from RM Circle: a wallet WITHOUT an on-chain member id still gets
+// a session — free members exist site-side only until their payout activation
+// or first purchase writes them on-chain (spec §4).
+const fs = require('fs');
+const path = require('path');
+const crypto = require('crypto');
+const { keccak256 } = require('./vendor/sha3');
+const secp = require('./vendor/secp256k1');
+
+let DATA_DIR = null;
+let chain = null;
+let IS_PROD = false;
+let SITE = 'instantadpay.com';
+
+const CHALLENGE_TTL = 10 * 60 * 1000;
+const SESSION_TTL = 30 * 24 * 60 * 60 * 1000; // 30 days
+const challenges = new Map(); // addressLower -> {message, exp}
+let sessions = new Map();     // token -> {address, memberId, expires}
+
+const SESS_FILE = () => path.join(DATA_DIR, 'sessions.json');
+function loadSessions() {
+  try {
+    const o = JSON.parse(fs.readFileSync(SESS_FILE(), 'utf8'));
+    sessions = new Map(Object.entries(o).filter(([, s]) => s.expires > Date.now()));
+  } catch (e) { sessions = new Map(); }
+}
+function saveSessions() {
+  try {
+    const tmp = SESS_FILE() + '.tmp';
+    fs.writeFileSync(tmp, JSON.stringify(Object.fromEntries(sessions)), { mode: 0o600 });
+    fs.renameSync(tmp, SESS_FILE());
+  } catch (e) { console.error('session save failed', e.message); }
+}
+
+function init(opts) {
+  DATA_DIR = opts.dataDir; chain = opts.chain; IS_PROD = !!opts.isProd;
+  if (opts.site) SITE = opts.site;
+  loadSessions();
+}
+
+// ---- crypto ----
+function personalDigest(msg) {
+  const m = Buffer.from(msg, 'utf8');
+  const pre = Buffer.from('\x19Ethereum Signed Message:\n' + m.length, 'utf8');
+  return Buffer.from(keccak256(Buffer.concat([pre, m])), 'hex');
+}
+function recoverAddress(msg, signature) {
+  const raw = Buffer.from(String(signature).replace(/^0x/, ''), 'hex');
+  if (raw.length !== 65) throw new Error('Bad signature length');
+  let v = raw[64]; if (v >= 27) v -= 27;
+  if (v !== 0 && v !== 1) throw new Error('Bad signature recovery byte');
+  const pub = secp.recoverPublicKey(personalDigest(msg), raw.slice(0, 64), v, false);
+  return '0x' + keccak256(Buffer.from(pub.slice(1))).slice(-40);
+}
+const ADDR_RE = /^0x[0-9a-fA-F]{40}$/;
+function checksumAddress(address) {
+  const a = address.toLowerCase().replace(/^0x/, '');
+  const h = keccak256(a);
+  let out = '0x';
+  for (let i = 0; i < a.length; i++) out += parseInt(h[i], 16) >= 8 ? a[i].toUpperCase() : a[i];
+  return out;
+}
+
+// ---- auth flow ----
+function makeChallenge(address) {
+  if (!ADDR_RE.test(address || '')) return { error: 'Bad address' };
+  const a = address.toLowerCase();
+  const nonce = crypto.randomBytes(16).toString('hex');
+  const chainId = chain.getConfig().chainId;
+  const message = `${SITE} wants you to sign in with your Ethereum account:\n${checksumAddress(a)}\n\nInstantAdPay member sign-in. This signature is free and cannot move funds or approve anything.\n\nURI: https://${SITE}\nVersion: 1\nChain ID: ${chainId}\nNonce: ${nonce}\nIssued At: ${new Date().toISOString()}`;
+  challenges.set(a, { message, exp: Date.now() + CHALLENGE_TTL });
+  return { message };
+}
+async function verifyChallenge(address, signature) {
+  const a = (address || '').toLowerCase();
+  const ch = challenges.get(a);
+  if (!ch || ch.exp < Date.now()) return { error: 'Challenge expired - tap sign-in again.' };
+  let rec;
+  try { rec = recoverAddress(ch.message, signature); } catch (e) { return { error: 'Invalid signature: ' + e.message }; }
+  if (rec !== a) return { error: 'Your wallet signed with a different account than the page is using ('
+    + rec.slice(0, 6) + '…' + rec.slice(-4) + '). Switch accounts and tap sign-in again.' };
+  challenges.delete(a);
+  let memberId = 0;
+  try { memberId = await chain.memberIdByAccount(a); } catch (e) { /* chain read down: session still valid */ }
+  const token = crypto.randomBytes(32).toString('hex');
+  sessions.set(token, { address: a, memberId, expires: Date.now() + SESSION_TTL });
+  saveSessions();
+  return { token, address: a, memberId };
+}
+function sessionCookie(token) {
+  return `iap.sid=${encodeURIComponent(token)}; Path=/; HttpOnly; SameSite=Lax; Max-Age=${SESSION_TTL / 1000}${IS_PROD ? '; Secure' : ''}`;
+}
+function clearCookie() { return 'iap.sid=; Path=/; HttpOnly; SameSite=Lax; Max-Age=0'; }
+function fromRequest(req) {
+  const m = /(?:^|;\s*)iap\.sid=([^;]+)/.exec(req.headers.cookie || '');
+  if (!m) return null;
+  const token = decodeURIComponent(m[1]);
+  const s = sessions.get(token);
+  if (!s || s.expires < Date.now()) return null;
+  return Object.assign({ token }, s);
+}
+async function refreshMemberId(sess) {
+  // called after an on-chain action so the session learns its new member id
+  try {
+    const id = await chain.memberIdByAccount(sess.address);
+    if (id && id !== sess.memberId) { sess.memberId = id; sessions.set(sess.token, {
+      address: sess.address, memberId: id, expires: sess.expires }); saveSessions(); }
+    return id;
+  } catch (e) { return sess.memberId; }
+}
+function logout(req) {
+  const s = fromRequest(req);
+  if (s) { sessions.delete(s.token); saveSessions(); }
+}
+
+module.exports = { init, makeChallenge, verifyChallenge, sessionCookie, clearCookie, fromRequest, refreshMemberId, logout };