REST API Developer & Backend Architect

Engineering Scalable, Secure Backend APIs

Santosh Gautam architectures secure and high-speed API layers. By writing low-latency routes in Node.js and Slim PHP, designing secure token authentication middleware, validating payloads, and configuring asynchronous webhook listeners for integrations, he provides robust backend connections. These APIs communicate directly with modern frontends built in React.js and Vue.js to deliver responsive, data-driven applications.

API Security Implementations & Token Management

Modern API development demands strict security controls at every endpoint. To protect against malicious intrusion, I configure strict Cross-Origin Resource Sharing (CORS) rules using origin whitelists, pre-flight options caches, and secure header structures. For user authentication, I build stateless token verification systems using JSON Web Tokens (JWT). The system issues a short-lived access token (expiring in 15 minutes) and a cryptographically signed refresh token (expiring in 7 days). This refresh token is stored inside an HttpOnly, Secure, and SameSite=Strict cookie, protecting the token from extraction via Cross-Site Scripting (XSS) and mitigating Cross-Site Request Forgery (CSRF).

To manage refresh token hijacking, a token rotation database log tracks every generation event. If a refresh token is used twice, the entire token family is immediately revoked, forcing all active devices to re-authenticate. Rate-limiting is handled at the proxy or application layer using Redis token-bucket algorithms. These limit requests to a strict threshold (e.g., 100 requests/minute per IP/API token), preventing Distributed Denial of Service (DDoS) attempts.

Asynchronous Webhook Security & Integrations

Integrating external services such as payment platforms (Stripe, PayU) or notification networks (WhatsApp Business API) requires reliable webhook ingestion. To protect backend routes, webhook receivers validate request headers cryptographically using HMAC signatures. Once authenticated, payload files are routed immediately to background message tables, returning a 200 OK response under 50ms and preventing connection timeouts.

For cryptographic validation, I build verification middleware using the API's raw request body. Computing the HMAC SHA256 digest on the raw buffer and comparing it against the provided signature header prevents timing attacks. Once validated, the webhook payload is parsed and saved directly into a queue broker. An independent background worker processes the queue, ensuring heavy webhook traffic does not degrade API endpoint latency.

Real-World Signature Verification Examples

Two shipped examples show this in practice. The WooCommerce Payment Gateway Boilerplate validates every inbound payment callback using a SHA-512 hash comparison via PHP's hash_equals(), preventing timing attacks on IPN webhook payloads. The WhatsApp Webhook Node.js guide documents the same principle in Node.js — HMAC-SHA256 signature verification combined with per-number rate limiting to block spoofed or excessive webhook traffic.

Performance Tuning and Caching Metrics

Optimizing API latency requires caching and query optimization. Read operations are intercepted by a Redis cache layer, which returns pre-computed responses in **under 2ms**. This enables the backend to achieve a **sub-80ms API response via Redis** even under heavy loads. Database transactions are protected with strict indexes on foreign key relations, keeping query runtimes consistently low. On the frontend, this performance supports a **Largest Contentful Paint (LCP) < 2.0s**, since static landing views display immediately while dynamic API requests resolve seamlessly.

// verifyWebhook.js - HMAC SHA256 Webhook Signature Verification middleware
const crypto = require('crypto');

module.exports = (secret) => {
  return (req, res, next) => {
    const signature = req.headers['x-signature'];
    if (!signature) {
      return res.status(401).json({ error: 'Signature header missing' });
    }

    // Compute Hash using raw request body buffer
    const hmac = crypto.createHmac('sha256', secret);
    const computedHash = hmac.update(req.rawBody).digest('hex');

    // Prevent timing attacks using crypto.timingSafeEqual
    const isSignatureValid = crypto.timingSafeEqual(
      Buffer.from(signature, 'utf8'),
      Buffer.from(computedHash, 'utf8')
    );

    if (!isSignatureValid) {
      return res.status(403).json({ error: 'Invalid payload signature' });
    }

    next();
  };
};