fix(security): add rate limiting for OTP endpoints

- Add verifyOtpLimiter: 5 attempts per 15 minutes per email/IP
- Add requestOtpLimiter: 3 attempts per 15 minutes per email/IP
- Use email as primary key, fallback to IP
- Return JSON error messages for rate limit exceeded

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/src/routes/auth.js

@@ -2,10 +2,39 @@ const express = require('express');
 const router = express.Router();
 const crypto = require('crypto');
 const jwt = require('jsonwebtoken');
+const rateLimit = require('express-rate-limit');
 const { supabase } = require('../config/supabase');
 const { sendOTPEmail } = require('../services/email');
 const storage = require('../services/storage');
 
+// Rate limiter for OTP verification: 5 attempts per 15 minutes per email/IP
+const verifyOtpLimiter = rateLimit({
+  windowMs: 15 * 60 * 1000, // 15 minutes
+  max: 5,
+  keyGenerator: (req) => {
+    // Use email if provided, otherwise fall back to IP
+    const email = req.body?.email?.toLowerCase()?.trim();
+    return email || req.ip;
+  },
+  message: { error: 'Too many verification attempts. Please try again in 15 minutes.' },
+  standardHeaders: true,
+  legacyHeaders: false,
+});
+
+// Rate limiter for OTP request: 3 attempts per 15 minutes per email/IP
+const requestOtpLimiter = rateLimit({
+  windowMs: 15 * 60 * 1000, // 15 minutes
+  max: 3,
+  keyGenerator: (req) => {
+    // Use email if provided, otherwise fall back to IP
+    const email = req.body?.email?.toLowerCase()?.trim();
+    return email || req.ip;
+  },
+  message: { error: 'Too many OTP requests. Please try again in 15 minutes.' },
+  standardHeaders: true,
+  legacyHeaders: false,
+});
+
 /**
  * POST /api/auth/check-email
  * Проверяет существует ли пользователь с данным email
@@ -49,8 +78,9 @@ router.post('/check-email', async (req, res) => {
  * POST /api/auth/request-otp
  * Отправляет OTP код на email
  * Если пользователя нет - создаёт нового
+ * Rate limited: 3 requests per 15 minutes per email/IP
  */
-router.post('/request-otp', async (req, res) => {
+router.post('/request-otp', requestOtpLimiter, async (req, res) => {
   try {
     const { email } = req.body;
 
@@ -137,8 +167,9 @@ router.post('/request-otp', async (req, res) => {
 /**
  * POST /api/auth/verify-otp
  * Проверяет OTP код и возвращает JWT токен
+ * Rate limited: 5 attempts per 15 minutes per email/IP
  */
-router.post('/verify-otp', async (req, res) => {
+router.post('/verify-otp', verifyOtpLimiter, async (req, res) => {
   try {
     const { email, code } = req.body;