JWT in Practice – Part 2: Refresh Tokens, Expiration, and Best Practices

After understanding the basics of JWT, it’s time to tackle the next level:

how to use it securely and sustainably in real-world applications.

1. Token Expiration: Why It Matters

JWTs should always have an expiration time (exp claim).

A token that never expires is a security risk — if leaked, it grants unlimited access.

Recommended Strategy:

• Short lifespan for access tokens (e.g., 15 minutes)
• Use a separate refresh token to extend sessions

This balances security with user experience.

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2. What is a Refresh Token?

A refresh token is a long-lived token used to request a new access token once the old one expires.

It’s:

• Stored securely (often in HttpOnly cookies)
• Sent to a secure endpoint like /auth/refresh
• Used only for refreshing, never for accessing resources directly

Flow Example:

1. User logs in → gets accessToken + refreshToken
2. Access token expires after 15 min
3. App sends refresh token to /auth/refresh
4. Server verifies and issues a new access token

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3. Best Practices for Secure JWT Usage

✅ Keep tokens small

Avoid adding too many claims — JWTs are sent on every request.

✅ Use HTTPS

Always transmit tokens over encrypted channels.

✅ Store tokens safely

• Access token: memory or secure client-side store
• Refresh token: HttpOnly, Secure Cookie

✅ Rotate refresh tokens

Issue a new refresh token with every use and invalidate the old one (prevent replay attacks).

✅ Allow token revocation

Use server-side blacklists or token identifiers (jti) with a Redis store for revoking stolen tokens.

✅ Validate everything

Always:

• Verify the signature
• Check expiration (exp)
• Confirm audience (aud) and issuer (iss), if used

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4. Bonus Tip: Split Your Auth Logic

Keep endpoints like /login, /refresh, /logout isolated from your core app logic.

This makes auth easier to test, monitor, and evolve over time.

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Final Thoughts

A secure authentication flow isn’t about choosing between “JWT or sessions” —

it’s about understanding trade-offs and building accordingly.

JWT can be incredibly powerful when paired with proper expiration and refresh logic.

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Want a real example in .NET or Node.js?

Let me know and I’ll share an implementation guide.

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