feat(multiuser): phase 2, multi-user auth pipeline

Adds a parallel multi-user auth branch (the single-user Basic-auth path is
left byte-identical). Off unless CODEMAN_MULTIUSER/--multiuser.

- middleware/auth.ts: mode-selecting registerAuthMiddleware. New async
  multi-user hook verifies username:password against the user store (scrypt),
  mints identity-carrying cookies, decorates req.authUser, enforces a per-IP
  AND per-username failure bucket, and the mustChangePassword lockbox. The
  hook-secret loopback bypass is now a single shared helper used by both
  branches. FastifyRequest.authUser module augmentation.
- ports/auth-port.ts: AuthSessionRecord gains username/role/mustChangePassword.
- user-store.ts: verifyPassword (timing-equalized against user enumeration).
- route-helpers.ts: getAuthUser (synthetic admin fallback), canAccessOwned,
  requireAdmin, revokeUserSessions; findSessionOrFail gains an optional req for
  a NOT_FOUND owner check (dormant until phase 3 wires callers).
- routes/me-routes.ts: GET /api/me (synthetic admin in single-user) and
  POST /api/me/password (verify current, min 8, clear mustChangePassword,
  revoke other sessions).
- QR: QrTokenRecord + AuthSessionRecord carry a username; tunnel-manager
  mintUserToken / consumeTokenWithIdentity / getQrSvgForCode; /q/:code binds
  the cookie to the token's user (rejects identity-less tokens in multi-user);
  GET /api/tunnel/qr mints a per-user token. Single-user keeps the rotating token.
- server.ts: bootstrap the initial admin from CODEMAN_USERNAME/PASSWORD on first
  boot (refuse to start with no users); multi-user with >= 1 user satisfies the
  non-loopback auth requirement and the tunnel-enable guard; userFailures bucket
  disposal.
- types/api.ts: FORBIDDEN, PASSWORD_CHANGE_REQUIRED, USER_EXISTS, USER_NOT_FOUND,
  LAST_ADMIN error codes (message + status wired).
- Session.owner field + getter/setter, SessionState.owner, MuxSession.owner,
  CreateSessionOptions.owner (foundation for phase 3 ownership threading).

Tests: test/multiuser-auth.test.ts (10, live server on 3170/3171). Existing auth
suite (auth-security, qr-auth, cod54-hook-event, network-auth-policy) unchanged
and green; full test:ci sweep passes (3519 tests).

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

src/web/routes/system-routes.ts

@@ -15,6 +15,9 @@ import { randomBytes } from 'node:crypto';
 import { dataPath } from '../../config/instance.js';
 import { ApiErrorCode, createErrorResponse, getErrorMessage, type NiceConfig } from '../../types.js';
 import { isUnauthenticatedNetworkAcknowledged } from '../network-auth-policy.js';
+import { isMultiUserMode } from '../../config/multiuser.js';
+import { findUser } from '../../user-store.js';
+import { getAuthUser } from '../route-helpers.js';
 import {
   ConfigUpdateSchema,
   SettingsUpdateSchema,
@@ -159,12 +162,19 @@ export function registerSystemRoutes(
     };
   });
 
-  app.get('/api/tunnel/qr', async (_req, reply) => {
+  app.get('/api/tunnel/qr', async (req, reply) => {
     const url = ctx.tunnelManager.getUrl();
     if (!url) {
       return reply.code(404).send(createErrorResponse(ApiErrorCode.NOT_FOUND, 'Tunnel not running'));
     }
     try {
+      if (isMultiUserMode()) {
+        // A rotating global token cannot carry identity — mint a single-use token
+        // bound to the requesting user so the scanned code logs THEM in.
+        const shortCode = ctx.tunnelManager.mintUserToken(getAuthUser(req).username);
+        const svg = await ctx.tunnelManager.getQrSvgForCode(url, shortCode);
+        return { svg, authEnabled: true };
+      }
       const authPassword = process.env.CODEMAN_PASSWORD;
       if (authPassword) {
         // Auth enabled — use cached SVG with embedded short code
@@ -188,10 +198,11 @@ export function registerSystemRoutes(
 
   app.get('/q/:code', async (req, reply) => {
     const shortCode = (req.params as { code: string }).code;
+    const multiUser = isMultiUserMode();
     const authPassword = process.env.CODEMAN_PASSWORD;
 
-    // No point if auth isn't enabled — just redirect
-    if (!authPassword) {
+    // No point if auth isn't enabled — just redirect. Multi-user is always "enabled".
+    if (!multiUser && !authPassword) {
       return reply.redirect('/');
     }
 
@@ -203,12 +214,26 @@ export function registerSystemRoutes(
       return reply.code(429).send('Too Many Requests');
     }
 
-    // Validate and atomically consume the token
-    if (!shortCode || !ctx.tunnelManager.consumeToken(shortCode)) {
+    // Validate and atomically consume the token (with any bound identity).
+    const consumed = shortCode ? ctx.tunnelManager.consumeTokenWithIdentity(shortCode) : { ok: false };
+    // In multi-user mode a token MUST carry an identity (an identity-less rotating
+    // token can't create a scoped session), so reject those too.
+    if (!consumed.ok || (multiUser && !consumed.username)) {
       ctx.qrAuthFailures?.set(clientIp, qrFailures + 1);
       return reply.code(401).send('Invalid or expired QR code');
     }
 
+    // Resolve the role for the bound user (disabled/deleted users fail closed).
+    let identity: { username: string; role: 'admin' | 'user' } | undefined;
+    if (multiUser && consumed.username) {
+      const user = await findUser(consumed.username);
+      if (!user || user.disabled) {
+        ctx.qrAuthFailures?.set(clientIp, qrFailures + 1);
+        return reply.code(401).send('Invalid or expired QR code');
+      }
+      identity = { username: user.username, role: user.role };
+    }
+
     // Issue session cookie (same pattern as Basic Auth success path)
     const sessionToken = randomBytes(32).toString('hex');
     const clientUA = req.headers['user-agent'] ?? '';
@@ -217,6 +242,9 @@ export function registerSystemRoutes(
       ua: clientUA,
       createdAt: Date.now(),
       method: 'qr',
+      username: identity?.username,
+      role: identity?.role,
+      mustChangePassword: false,
     });
     ctx.qrAuthFailures?.delete(clientIp);
 
@@ -585,7 +613,10 @@ export function registerSystemRoutes(
     // letting an operator opt in from the browser without setting the env var.
     // Guard runs BEFORE persisting so a refused tunnelEnabled:true is not saved.
     if (settings.tunnelEnabled === true && !ctx.tunnelManager.isRunning()) {
-      const acknowledged = isUnauthenticatedNetworkAcknowledged() || settings.acknowledgeUnauthTunnel === true;
+      // Multi-user mode makes the tunnel authenticated (every person has their own
+      // credential), so it satisfies the same requirement as CODEMAN_PASSWORD.
+      const acknowledged =
+        isMultiUserMode() || isUnauthenticatedNetworkAcknowledged() || settings.acknowledgeUnauthTunnel === true;
       if (!acknowledged) {
         const msg =
           'Refusing to start the Cloudflare tunnel without authentication: it would publish ' +