fixed security in /backend/index.js

[imanojgaur]

Description

Please include a summary of the changes and the related issue. Also include any relevant motivation and context.

Fixes # (issue)

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce.

• Unit tests
• Integration tests
• Manual testing

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

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[Copilot]

Pull Request Overview

This PR implements security hardening for the backend Express.js application by adding essential security middleware and configuration. The changes address multiple security vulnerabilities including XSS protection, rate limiting, input sanitization, and CORS configuration.

• Added comprehensive security middleware (Helmet, XSS-clean, mongo-sanitize, rate limiting)
• Implemented environment variable validation and improved CORS configuration
• Restructured application initialization to apply security measures before route setup

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[Copilot]

The CORS origin configuration allows an empty array as fallback, which would block all origins. Consider using a secure default like ['http://localhost:3000'] for development or require CORS_ORIGIN to be explicitly set in production.

Suggested change

	const corsOptions = {
	origin: process.env.CORS_ORIGIN?.split(',') || [],
	let allowedOrigins;
	if (process.env.NODE_ENV === 'production') {
	if (!process.env.CORS_ORIGIN) {
	console.error('❌ Missing required env var: CORS_ORIGIN in production');
	process.exit(1);
	}
	allowedOrigins = process.env.CORS_ORIGIN.split(',');
	} else {
	allowedOrigins = process.env.CORS_ORIGIN
	? process.env.CORS_ORIGIN.split(',')
	: ['http://localhost:3000'];
	}
	const corsOptions = {
	origin: allowedOrigins,

[Copilot]

The error handler logs the full error stack to console, which could expose sensitive information in production logs. Consider logging less detailed information in production environments by checking NODE_ENV.

Suggested change

	console.error(err.stack);
	if (process.env.NODE_ENV !== 'production') {
	console.error(err.stack);
	} else {
	console.error('Error:', err.message);
	}

[Copilot]

The rate limiting configuration uses magic numbers. Consider moving these values to environment variables (e.g., AUTH_RATE_LIMIT_WINDOW_MS, AUTH_RATE_LIMIT_MAX) for better configurability across different environments.

Suggested change

	windowMs: 15 * 60 * 1000,
	max: 10,
	windowMs: parseInt(process.env.AUTH_RATE_LIMIT_WINDOW_MS, 10) || 15 * 60 * 1000,
	max: parseInt(process.env.AUTH_RATE_LIMIT_MAX, 10) || 10,