Token Expiration and Refresh Strategies in JWT Authentication Quiz

Explore essential best practices for handling token expiration and refresh strategies in JWT and token-based authentication. Assess your understanding of secure token lifecycles, refresh token management, and common pitfalls in security testing for modern authentication systems.

1. Short-Lived vs Long-Lived Tokens

   Why is it recommended to use short-lived access tokens combined with refresh tokens in a JWT-based authentication system?

   1. Short-lived tokens reduce the risk of misuse if compromised, while refresh tokens allow seamless re-authentication.
   2. Long-lived tokens enhance user experience by never requiring renewal.
   3. Short-lived tokens make brute force attacks more common.
   4. Refresh tokens should be used alone for maximum security.

   Explanation: Short-lived access tokens limit the window an attacker has if a token is compromised, thereby reducing risk. Refresh tokens allow users to obtain new access tokens without frequent logins, balancing security and usability. Long-lived tokens can increase risk because they provide attackers with prolonged access. Using only refresh tokens for authentication is insecure, as it isn't their intended use and may increase attack surface.

2. Refresh Token Storage Practices

   In a web application, which is the most secure way to store refresh tokens on the client side to minimize exposure to cross-site scripting (XSS) attacks?

   1. Store refresh tokens in an httpOnly, secure cookie.
   2. Store refresh tokens in localStorage.
   3. Hold refresh tokens in a JavaScript variable in memory.
   4. Embed refresh tokens into the HTML source code.

   Explanation: Storing refresh tokens in httpOnly, secure cookies helps protect them from JavaScript access and ensures they are only sent to trusted origins over HTTPS, significantly reducing XSS risk. LocalStorage is vulnerable to XSS attacks, while JavaScript variables do not persist across browser reloads and are still accessible by scripts. Embedding tokens in HTML exposes them directly to anyone with page access, making it very insecure.

3. Detection of Expired Tokens

   What should a properly implemented API do when a client presents an expired JWT access token during an authenticated request?

   1. Reject the request with an unauthorized error and prompt the client to use a refresh token.
   2. Automatically extend the expiration of the access token.
   3. Allow the request if it was signed with a valid secret.
   4. Silently accept the token and proceed as if it were valid.

   Explanation: The correct response is to reject requests with expired tokens, signaling the client to use a refresh token for obtaining a new access token. Automatically extending the expiration is insecure and undermines token lifecycle management. Accepting requests based solely on a valid signature, disregarding expiration, exposes the system to replay attacks. Silently accepting expired tokens defeats the purpose of token expiration.

4. Refreshing and Revoking Tokens

   When implementing a refresh token mechanism, which strategy best supports the ability to revoke tokens if a user logs out or changes credentials?

   1. Store refresh tokens with a backend tracking method for explicit revocation.
   2. Allow refresh tokens to exist only in client memory.
   3. Issue non-expiring refresh tokens without server-side control.
   4. Always reissue the same refresh token after every request.

   Explanation: Backend tracking (such as a token allowlist or blacklist) allows the server to invalidate refresh tokens upon logout or credential changes, supporting secure revocation. Storing tokens only in memory loses control over persistence and fails on browser reloads. Non-expiring, uncontrolled tokens can't be revoked, introducing risk. Reissuing the same refresh token allows attackers prolonged access if one is ever stolen.

5. Token Rotation and Replay Prevention

   Why is rotating refresh tokens on every use a recommended practice for preventing replay attacks in JWT-based systems?

   1. It ensures that a used refresh token becomes invalid after redemption, limiting reuse.
   2. It increases the length of the token, making it harder to guess.
   3. It automatically grants additional permissions with each rotation.
   4. It reduces the number of tokens a user ever needs to store.

   Explanation: Rotating refresh tokens on each use makes the previous token invalid, preventing attackers from using intercepted refresh tokens for re-authentication. Increasing token length does not address replay risks. Granting additional permissions on rotation is insecure and not standard. Reducing the number of tokens stored is unrelated to replay protection and could lower security if not managed carefully.