How to Implement JWT Authentication

The security patterns tutorials skip - and attackers dont.

JWT authentication is one of the most commonly implemented and most commonly misconfigured auth patterns in web development. This guide covers access/refresh token architecture, secure storage, rotation strategy, and the revocation approach that doesnt require a database query on every request.

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Access Token vs Refresh Token - Why Both?

Short-lived access tokens (15 minutes) limit the blast radius of a stolen token. Long-lived refresh tokens (7-30 days) provide session continuity without requiring re-login. The combination gives you security without friction. The flow: client stores refresh token in an httpOnly cookie (not localStorage), access token in memory. On expiry client calls /auth/refresh with the cookie - server issues a new access token. If the refresh token is stolen, rotation detection catches it.

At Valletta Software, we focus on:

Access token: short-lived (15min) stored in memory - never in localStorage

Refresh token: long-lived (7-30 days) stored in httpOnly secure cookie - not accessible to JS

Token rotation: issue a new refresh token on every use - detect reuse as compromise signal

Revocation: maintain a revoked token blocklist in Redis - check on refresh only not every request

Payload: userId role tokenVersion - nothing sensitive it is not encrypted

Algorithm: RS256 (asymmetric) for distributed verification HS256 only for single-service

Logout: invalidate the refresh token server-side - client-side token deletion is not enough

The Security Mistakes That Get Teams Breached

Each of these is in a real production application right now.

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localStorage for JWTs: accessible to any XSS - httpOnly cookie only for refresh tokens

No expiry: tokens that never expire are permanent backdoors

No rotation: stolen refresh token equals permanent session - implement rotation and reuse detection

Sensitive data in payload: JWT is base64 not encrypted - user email visible to anyone with the token

Missing algorithm validation: accept none algorithm - always explicitly set and validate alg

Weak secret: HS256 with a short secret is brutable - 256+ bit secret or use RS256

No CSRF protection: if using cookies add CSRF token or SameSite=Strict

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How to Implement JWT Authentication - With Engineers Who Do Security Right

Our backend engineers implement JWT auth with rotation revocation httpOnly cookies and RS256 signing - not the tutorial version that gets breached in 6 months.

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Our backend engineers implement JWT auth with access/refresh token architecture, httpOnly cookies, token rotation, Redis-based revocation, and RS256 signing.

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