fix(auth): handle requires_webauthn in POST /login — was a 500 self-lockout

authService.login returns a requires_webauthn payload for webauthn-enabled
users, but the login route only handled requires_totp and fell through to
result.user.id (undefined) -> TypeError -> 500 on every attempt. Any user who
enabled WebAuthn via the API (reachable today) was permanently locked out.

- routes/auth.cts: return the two-step requires_webauthn payload (mirrors TOTP)
- services/authService.cts: stale-flag guard — webauthn_enabled with no usable
  credentials falls through to password login instead of hard-failing
- tests/authLoginWebauthnRoute.test.js: pins both paths + wrong-password 401

(QA-B1-01, lockout part)

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

routes/auth.cts

@@ -99,6 +99,16 @@ router.post(
         return res.json({ requires_totp: true, challenge_token: result.challenge_token });
       }
 
+      // WebAuthn required — same two-step shape as TOTP; the session is only
+      // created after POST /webauthn/challenge verifies the key.
+      if (result.requires_webauthn) {
+        return res.json({
+          requires_webauthn: true,
+          challenge_token: result.challenge_token,
+          webauthn_options: result.webauthn_options,
+        });
+      }
+
       logAudit({
         user_id: result.user.id,
         action: 'login.success',

services/authService.cts

@@ -89,9 +89,17 @@ async function login(username: any, password: any) {
       createAuthenticationChallenge,
       createLoginChallenge,
     } = require('./webauthnService.cts');
-    const { options, challengeId } = await createAuthenticationChallenge(getDb(), user.id);
-    const loginToken = createLoginChallenge(getDb(), user.id, challengeId);
-    return { requires_webauthn: true, challenge_token: loginToken, webauthn_options: options };
+    try {
+      const { options, challengeId } = await createAuthenticationChallenge(getDb(), user.id);
+      const loginToken = createLoginChallenge(getDb(), user.id, challengeId);
+      return { requires_webauthn: true, challenge_token: loginToken, webauthn_options: options };
+    } catch (err: any) {
+      // Stale flag (enabled but no usable credentials): a hard failure here would
+      // lock the account out entirely — fall through to password-only login instead.
+      log.warn(
+        `[auth] WebAuthn enabled for user ${user.id} but challenge creation failed (${err.message}); proceeding with password login`,
+      );
+    }
   }
 
   // Clean up expired sessions for this user before creating new session

tests/authLoginWebauthnRoute.test.js

@@ -0,0 +1,129 @@
+'use strict';
+
+// QA-B1-01 — POST /login for a webauthn-enabled user must return the
+// requires_webauthn two-step payload (not fall through and 500), and a user
+// whose webauthn_enabled flag is stale (no credential rows) must still be able
+// to log in with their password instead of being locked out.
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const os = require('node:os');
+const path = require('node:path');
+const fs = require('node:fs');
+
+const dbPath = path.join(os.tmpdir(), `bill-tracker-webauthn-login-${process.pid}.sqlite`);
+process.env.DB_PATH = dbPath;
+
+const { getDb, closeDb } = require('../db/database.cts');
+const { hashPassword } = require('../services/authService.cts');
+const router = require('../routes/auth.cts');
+
+const PASSWORD = 'correct-horse-battery';
+
+function handler(method, routePath) {
+  const layer = router.stack.find((l) => l.route?.path === routePath && l.route.methods[method]);
+  assert.ok(layer, `${method.toUpperCase()} ${routePath} exists`);
+  return layer.route.stack[layer.route.stack.length - 1].handle;
+}
+
+function callLogin(body) {
+  const h = handler('post', '/login');
+  return new Promise((resolve, reject) => {
+    const req = {
+      body,
+      ip: '127.0.0.1',
+      cookies: {},
+      headers: {},
+      secure: false,
+      get: () => 'node-test-agent',
+    };
+    const cookies = [];
+    const res = {
+      statusCode: 200,
+      status(code) {
+        this.statusCode = code;
+        return this;
+      },
+      cookie(name, value, opts) {
+        cookies.push({ name, value, opts });
+      },
+      json(data) {
+        resolve({ status: this.statusCode, body: data, cookies });
+      },
+    };
+    Promise.resolve(h(req, res)).catch(reject);
+  });
+}
+
+let webauthnUserId;
+let staleFlagUserId;
+
+test.before(async () => {
+  const db = getDb();
+  const hash = await hashPassword(PASSWORD);
+
+  const u1 = db
+    .prepare(
+      "INSERT INTO users (username, password_hash, role, webauthn_enabled) VALUES (?, ?, 'user', 1)",
+    )
+    .run('webauthn-user', hash);
+  webauthnUserId = u1.lastInsertRowid;
+  db.prepare(
+    'INSERT INTO webauthn_credentials (user_id, credential_id, public_key, sign_count, transports) VALUES (?, ?, ?, 0, ?)',
+  ).run(webauthnUserId, 'dGVzdC1jcmVkLWlk', 'dGVzdC1wdWJsaWMta2V5', JSON.stringify(['internal']));
+
+  const u2 = db
+    .prepare(
+      "INSERT INTO users (username, password_hash, role, webauthn_enabled) VALUES (?, ?, 'user', 1)",
+    )
+    .run('stale-flag-user', hash);
+  staleFlagUserId = u2.lastInsertRowid;
+});
+
+test.after(() => {
+  closeDb();
+  for (const suffix of ['', '-shm', '-wal']) {
+    try {
+      fs.unlinkSync(dbPath + suffix);
+    } catch {}
+  }
+});
+
+test('webauthn-enabled user gets the two-step payload, not a 500', async () => {
+  const { status, body, cookies } = await callLogin({
+    username: 'webauthn-user',
+    password: PASSWORD,
+  });
+  assert.equal(status, 200);
+  assert.equal(body.requires_webauthn, true);
+  assert.equal(typeof body.challenge_token, 'string');
+  assert.ok(body.challenge_token.length > 0);
+  assert.ok(body.webauthn_options, 'webauthn_options present');
+  assert.equal(typeof body.webauthn_options.challenge, 'string');
+  assert.equal(cookies.length, 0, 'no session cookie before the key verifies');
+  assert.equal(body.user, undefined, 'no user payload before the key verifies');
+
+  const challenge = getDb()
+    .prepare(
+      "SELECT id FROM webauthn_challenges WHERE user_id = ? AND challenge_type = 'authentication'",
+    )
+    .get(webauthnUserId);
+  assert.ok(challenge, 'authentication challenge persisted');
+});
+
+test('stale webauthn flag (no credentials) falls through to password login, not lockout', async () => {
+  const { status, body, cookies } = await callLogin({
+    username: 'stale-flag-user',
+    password: PASSWORD,
+  });
+  assert.equal(status, 200);
+  assert.equal(body.requires_webauthn, undefined);
+  assert.ok(body.user, 'password login succeeded despite the stale flag');
+  assert.equal(body.user.id, staleFlagUserId);
+  assert.equal(cookies.length, 1, 'session cookie issued');
+});
+
+test('wrong password still 401s for a webauthn-enabled user', async () => {
+  const { status, body } = await callLogin({ username: 'webauthn-user', password: 'nope-wrong' });
+  assert.equal(status, 401);
+  assert.equal(body.code, 'AUTH_ERROR');
+});