🔑 About JWT (JSON Web Token)

  • JWT is a compact, URL-safe token format used for securely transmitting information between parties.
  • Each token is digitally signed (usually with HMAC or RSA), so it can be validated without querying the database — making authentication much faster.
  • Access Tokens are bearer tokens sent with every API request to one or more resource servers.
    • Typically stored in browser memory or local storage.
    • Susceptible to XSS attacks, but risk is reduced by keeping their lifespan short (e.g., 5–15 minutes).

Basic Format

🧭 Why a Two-Token Design (Access + Refresh)

Using two tokens instead of one long-lived token is a security best practice that balances user convenience and safety.

  • Single long-lived tokens pose major security risks:

    • If leaked, they allow persistent unauthorized access.
    • Revoking them requires server-side storage or blacklists, defeating JWT’s stateless nature.

  • Access Token

    • Short-lived and stateless — no DB lookup needed for validation.
    • Used to access protected resources quickly and efficiently.

  • Refresh Token

    • Long-lived and stored more securely (e.g., HTTP-only cookie or secure device keystore).
    • Sent only to the authorization server’s token endpoint to get a new access token.
    • Server checks if the refresh token is revoked or expired before issuing a new one.

🗄️ Where Tokens Are Stored

  • Refresh Tokens
    • Stored in a database table, enabling revocation and tracking.
  • Access Token Secrets / Keys
    • Stored securely in environment variables or key management services (e.g., AWS KMS, Vault).

⚖️ Benefits & Drawbacks

Aspect Two-Token Design Single-Token Design
Performance Fast access validation (no DB hit) Same, but risks persist
Security Safer — short-lived access, revocable refresh Risky — hard to revoke, long-lived compromise
Complexity Slightly higher (two-token flow) Simpler implementation
Scalability Stateless validation, scalable across services Can require DB checks if revocation added

🚫 Why Not Use a Single Token?

Using one long-lived JWT for both access and refresh purposes is dangerous because: - Compromise of the token means unlimited access until expiry. - You lose the ability to revoke compromised sessions. - You must choose between: - Short expiry: Poor UX (frequent logins) - Long expiry: Severe security risk

✅ Summary

A two-token system (Access + Refresh): - Keeps APIs fast (stateless JWT validation). - Enables token revocation and rotation for security. - Provides a safe, scalable authentication pattern ideal for distributed systems and microservices.