Building secure authentication is one of the most important responsibilities of backend developers today. With cyberattacks increasing, companies—even startups—expect developers to know how to build authentication systems that are safe, scalable, and production-ready. And one of the fastest ways to grab the attention of a technical recruiter is to show a backend project where authentication is implemented properly, not just with the basic “store JWT in localStorage” method.

But here's the truth most beginners don’t know: storing tokens in localStorage is not secure, especially for real-world apps. If your goal is to build a real backend in 2025—something that looks good on GitHub and your resume—then cookie-based authentication with access & refresh tokens is the way to go.

In this blog, we break down everything in a simple, human-friendly manner (Indian English tone), explain why cookies are safer, and walk through how a TypeScript backend handles a modern token-based login system.

Why Authentication Needs to Be Secure in 2025

Whether you are building an e-commerce backend, SaaS dashboard, internal tool, or even a portfolio project, authentication is one part recruiters check very seriously. They want to see:

• →You understand how JWT works
• →You know the risks of XSS & CSRF
• →You can build refresh-token rotation
• →You know how to protect APIs in production
• →You don’t store sensitive data in the browser

A backend with proper cookie-based authentication immediately signals professional engineering practices.

Let’s first understand the core issue with the old-school method.

Why Storing JWT Tokens in localStorage Is Not Safe

LocalStorage is convenient, yes. But convenience often sacrifices security.

❌ 1. localStorage Is Fully Accessible to JavaScript

This means:

If your site has any XSS vulnerability, attackers can simply run:

js
localStorage.getItem("access_token")

Boom. They now have full access to the user’s account.

This is why companies DO NOT allow storing JWTs in localStorage for production, especially in fintech, healthcare, and enterprise apps.

❌ 2. XSS Attacks Are Far More Common Than People Think

A single small mistake like:

• →Unescaped user input
• →Vulnerable third-party scripts
• →Uncontrolled HTML injection

…is enough for an attacker to steal your tokens.

❌ 3. Tokens in localStorage Never Expire Automatically

If someone steals the token, they can keep using it until it expires.

❌ 4. Browser Extensions Can Access localStorage

Extensions with the right permissions can read all localStorage values. (This is more common than you think.)

Why Cookie-Based Authentication Is More Secure

Modern backend engineers use HTTP-Only, Secure cookies to store tokens.

These cookies come with superpowers you don’t get in localStorage:

✔️ 1. JavaScript Cannot Access the Cookie

The flag:

HttpOnly

makes it invisible to JavaScript.

Even if your site has XSS vulnerability, attackers cannot steal the cookie.

✔️ 2. Protects Against Most Token-Theft Attacks

No JS access → No simple token stealing.

✔️ 3. Automatically Sent with Requests

You don’t manually attach cookies. Browsers handle it, making the developer's life easier and the system cleaner.

✔️ 4. Works Perfectly with Refresh Token Rotation

The refresh token stays safe inside httpOnly cookies, protected from external access.

When recruiters see cookies + refresh tokens, they understand you know the real stuff.

Understanding the Access Token + Refresh Token Workflow

A modern authentication system uses two tokens:

🔐 Access Token (short-lived)

• →Lifespan: 5–15 minutes
• →Sent with every API request
• →Used to verify the user quickly
• →If stolen, damage is limited due to short life

🔐 Refresh Token (long-lived)

• →Lifespan: Days or weeks
• →Stored only in HTTP-Only cookies
• →Used to create a new access token
• →Rotated regularly to reduce risk

When your access token expires, you automatically refresh it without forcing the user to log in again.

This creates a smooth UX + very strong security.

Full Authentication Flow (Explained Simply)

Here’s what happens during login:

1. →User logs in with email/password
2. →Backend verifies credentials
3. →Backend creates:
   • →Access token (short life)
   • →Refresh token (long life)
4. →Refresh token is stored in an HTTP-only secure cookie
5. →Access token is sent to the frontend (or also set in a cookie)
6. →User can now make authenticated requests
7. →When access token expires → frontend silently calls /refresh
8. →Backend validates refresh token from cookie
9. →New tokens are generated
10. →User continues without interruptions

This is the architecture used everywhere in production today.

TypeScript Example: Cookie-Based JWT Auth

Below is a small but professional-style backend example using Express + TypeScript:

ts
import express from "express";
import jwt from "jsonwebtoken";
import cookieParser from "cookie-parser";
import cors from "cors";

const app = express();
app.use(
  cors({
    origin: process.env.FRONTEND_URL!,
    credentials: true, // allow cookies
    methods: ["GET", "POST", "PUT", "DELETE"],
    allowedHeaders: ["Content-Type", "Authorization"],
    exposedHeaders: ["Authorization"],
  })
);
app.use(express.json());
app.use(cookieParser());

const ACCESS_SECRET = process.env.ACCESS_SECRET!;
const REFRESH_SECRET = process.env.REFRESH_SECRET!;

function generateTokens(payload: any) {
  const accessToken = jwt.sign(payload, ACCESS_SECRET, { expiresIn: "10m" });
  const refreshToken = jwt.sign(payload, REFRESH_SECRET, { expiresIn: "7d" });
  return { accessToken, refreshToken };
}

app.post("/login", (req, res) => {
  const { email, password } = req.body;

  // Dummy example
  if (email !== "test@example.com" || password !== "123456") {
    return res.status(401).json({ message: "Invalid credentials" });
  }

  const tokens = generateTokens({ email });

  res.cookie("refresh_token", tokens.refreshToken, {
    httpOnly: true,
    secure: true,
    sameSite: "strict",
    path: "/refresh"
  });

  return res.json({
    access_token: tokens.accessToken,
    message: "Login successful"
  });
});

app.post("/refresh", (req, res) => {
  const token = req.cookies.refresh_token;
  if (!token) return res.status(401).json({ message: "No refresh token" });

  try {
    const payload = jwt.verify(token, REFRESH_SECRET);
    const tokens = generateTokens({ email: payload.email });

    res.cookie("refresh_token", tokens.refreshToken, {
      httpOnly: true,
      secure: true,
      sameSite: "strict",
      path: "/refresh"
    });

    return res.json({ access_token: tokens.accessToken });
  } catch {
    return res.status(401).json({ message: "Invalid refresh token" });
  }
});

app.listen(3000, () => console.log("Server running on 3000"));

This is the exact pattern used in production-level apps.

Common Mistakes Beginners Make (and How to Avoid Them)

❌ Storing refresh tokens in localStorage

→ Always store in cookies.

❌ Using long-lived access tokens

→ Always keep them short-lived.

❌ Not rotating refresh tokens

→ Always generate a new one at each refresh.

❌ Sending tokens in response body unnecessarily

→ Keep sensitive parts in cookies whenever possible.

Best Practices for Secure Cookie-Based Auth

• →Use httpOnly + secure + sameSite=strict for all tokens
• →Use short access tokens
• →Use refresh token rotation
• →Implement logout by clearing cookies
• →Use CSRF tokens for extra-sensitive apps
• →Keep secrets in ${.env}
• →Use HTTPS in production

Mentioning these in your GitHub README or resume automatically improves your credibility.

Conclusion

If you're building a TypeScript backend in 2025, then cookie-based authentication with refresh + access tokens is the safest, cleanest, and most industry-validated way to authenticate users. It gives you:

• →Strong protection against XSS token theft
• →Automatic request handling via cookies
• →Smooth UX with silent token refresh
• →Full compatibility with React, Next.js, Angular, and native apps
• →A strong resume highlight for backend roles

So ditch the outdated localStorage method and upgrade your backend authentication like a true software engineer.

This one improvement can make your project stand out instantly — because secure authentication is what separates hobby projects from real-world, production-ready engineering.