feat: implement dynamic rate limiting with database configuration

- Add database migration for rate limit settings
- Create rate limit service with dynamic configuration from database
- Implement proper authentication detection for admin and gallery tokens
- Skip rate limiting for authenticated users (configurable)
- Add admin API endpoint to update rate limit settings
- Use correct client IP detection with proxy support
- Cache settings for performance (1 minute cache)
- Default to 1000 requests per 15 minutes for better UX
- Apply auth-specific limits only to login endpoints

Key improvements:
- No more rate limiting for authenticated gallery/admin users
- Configurable via admin settings page
- Immediate effect when settings change
- Better handling of proxied requests

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

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

backend/src/services/rateLimitService.js

@@ -0,0 +1,243 @@
+const rateLimit = require('express-rate-limit');
+const jwt = require('jsonwebtoken');
+const { db } = require('../database/db');
+const logger = require('../utils/logger');
+
+// Cache for rate limit settings
+let settingsCache = null;
+let cacheExpiry = 0;
+const CACHE_DURATION = 60000; // 1 minute cache
+
+/**
+ * Get rate limit settings from database with caching
+ */
+async function getRateLimitSettings() {
+  try {
+    // Check cache
+    if (settingsCache && Date.now() < cacheExpiry) {
+      return settingsCache;
+    }
+
+    // Fetch from database
+    const settings = await db('app_settings')
+      .whereIn('setting_key', [
+        'rate_limit_enabled',
+        'rate_limit_window_minutes',
+        'rate_limit_max_requests',
+        'rate_limit_auth_max_requests',
+        'rate_limit_skip_authenticated',
+        'rate_limit_public_endpoints_only'
+      ]);
+
+    // Parse settings into object
+    const config = {
+      enabled: true,
+      windowMinutes: 15,
+      maxRequests: 100,
+      authMaxRequests: 5,
+      skipAuthenticated: true,
+      publicEndpointsOnly: false
+    };
+
+    settings.forEach(setting => {
+      const value = JSON.parse(setting.setting_value);
+      switch (setting.setting_key) {
+      case 'rate_limit_enabled':
+        config.enabled = value;
+        break;
+      case 'rate_limit_window_minutes':
+        config.windowMinutes = value;
+        break;
+      case 'rate_limit_max_requests':
+        config.maxRequests = value;
+        break;
+      case 'rate_limit_auth_max_requests':
+        config.authMaxRequests = value;
+        break;
+      case 'rate_limit_skip_authenticated':
+        config.skipAuthenticated = value;
+        break;
+      case 'rate_limit_public_endpoints_only':
+        config.publicEndpointsOnly = value;
+        break;
+      }
+    });
+
+    // Update cache
+    settingsCache = config;
+    cacheExpiry = Date.now() + CACHE_DURATION;
+
+    return config;
+  } catch (error) {
+    logger.error('Failed to fetch rate limit settings:', error);
+    // Return defaults on error
+    return {
+      enabled: true,
+      windowMinutes: 15,
+      maxRequests: 100,
+      authMaxRequests: 5,
+      skipAuthenticated: true,
+      publicEndpointsOnly: false
+    };
+  }
+}
+
+/**
+ * Clear settings cache (call when settings are updated)
+ */
+function clearSettingsCache() {
+  settingsCache = null;
+  cacheExpiry = 0;
+}
+
+/**
+ * Check if request has valid authentication
+ */
+function isAuthenticated(req) {
+  try {
+    const authHeader = req.headers.authorization;
+    if (!authHeader || !authHeader.startsWith('Bearer ')) {
+      return false;
+    }
+
+    const token = authHeader.substring(7);
+    const decoded = jwt.verify(token, process.env.JWT_SECRET);
+    
+    // Check if token is valid
+    if (!decoded || typeof decoded !== 'object') {
+      return false;
+    }
+
+    // Valid token found - check type
+    req.tokenType = decoded.type; // 'admin' or 'gallery'
+    req.tokenPayload = decoded;
+    
+    return true;
+  } catch (error) {
+    return false;
+  }
+}
+
+/**
+ * Determine if rate limiting should be applied to this request
+ */
+function shouldSkipRateLimit(req, config) {
+  // If rate limiting is disabled globally
+  if (!config.enabled) {
+    return true;
+  }
+
+  // Never skip rate limiting for auth endpoints
+  const isAuthEndpoint = req.path.match(/\/(auth|login|gallery\/[^/]+\/verify)$/);
+  if (isAuthEndpoint) {
+    return false;
+  }
+
+  // Check if we should skip authenticated requests
+  if (config.skipAuthenticated && isAuthenticated(req)) {
+    return true;
+  }
+
+  // Check if we only rate limit public endpoints
+  if (config.publicEndpointsOnly) {
+    const isPublicEndpoint = req.path.startsWith('/api/public/') || 
+                           req.path.startsWith('/api/gallery/') ||
+                           isAuthEndpoint;
+    return !isPublicEndpoint;
+  }
+
+  return false;
+}
+
+/**
+ * Create dynamic rate limiter
+ */
+async function createRateLimiter() {
+  const config = await getRateLimitSettings();
+  
+  return rateLimit({
+    windowMs: config.windowMinutes * 60 * 1000,
+    max: async (req) => {
+      // Refresh config for each request
+      const currentConfig = await getRateLimitSettings();
+      
+      // Different limits for auth endpoints
+      const isAuthEndpoint = req.path.match(/\/(auth|login|gallery\/[^/]+\/verify)$/);
+      return isAuthEndpoint ? currentConfig.authMaxRequests : currentConfig.maxRequests;
+    },
+    keyGenerator: (req) => {
+      // Use correct client IP when behind proxy
+      return req.headers['x-forwarded-for']?.split(',')[0]?.trim() || 
+             req.headers['x-real-ip'] || 
+             req.connection.remoteAddress || 
+             req.ip;
+    },
+    skip: async (req) => {
+      const currentConfig = await getRateLimitSettings();
+      return shouldSkipRateLimit(req, currentConfig);
+    },
+    handler: (req, res) => {
+      const clientIp = req.headers['x-forwarded-for']?.split(',')[0]?.trim() || req.ip;
+      logger.warn('Rate limit exceeded', {
+        ip: clientIp,
+        path: req.path,
+        method: req.method,
+        authenticated: isAuthenticated(req),
+        tokenType: req.tokenType
+      });
+      
+      res.status(429).json({ 
+        error: 'Too many requests, please try again later.',
+        retryAfter: res.getHeader('Retry-After')
+      });
+    },
+    standardHeaders: true, // Return rate limit info in headers
+    legacyHeaders: false, // Disable X-RateLimit headers
+  });
+}
+
+/**
+ * Create auth-specific rate limiter
+ */
+async function createAuthRateLimiter() {
+  const config = await getRateLimitSettings();
+  
+  return rateLimit({
+    windowMs: config.windowMinutes * 60 * 1000,
+    max: config.authMaxRequests,
+    keyGenerator: (req) => {
+      // Use correct client IP when behind proxy
+      return req.headers['x-forwarded-for']?.split(',')[0]?.trim() || 
+             req.headers['x-real-ip'] || 
+             req.connection.remoteAddress || 
+             req.ip;
+    },
+    skip: async () => {
+      const currentConfig = await getRateLimitSettings();
+      return !currentConfig.enabled;
+    },
+    handler: (req, res) => {
+      const clientIp = req.headers['x-forwarded-for']?.split(',')[0]?.trim() || req.ip;
+      logger.warn('Auth rate limit exceeded', {
+        ip: clientIp,
+        path: req.path
+      });
+      
+      res.status(429).json({ 
+        error: 'Too many authentication attempts, please try again later.',
+        retryAfter: res.getHeader('Retry-After')
+      });
+    },
+    standardHeaders: true,
+    legacyHeaders: false,
+  });
+}
+
+module.exports = {
+  getRateLimitSettings,
+  clearSettingsCache,
+  createRateLimiter,
+  createAuthRateLimiter,
+  isAuthenticated,
+  shouldSkipRateLimit
+};