Spring Security 6 & JWT Authentication · Lesson

JWT Blacklisting and Whitelisting

Deep dive into advanced token revocation techniques, including maintaining blacklists or whitelists of tokens.

JWT Blacklisting and Whitelisting is a free Spring Security 6 & JWT Authentication lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Security 6 & JWT Authentication learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Why Revoke JWTs?

JSON Web Tokens (JWTs) are powerful for authentication, but sometimes you need to invalidate them before their natural expiry. This process is called token revocation.

Compromised Token: If a token is stolen.
User Logout: To immediately end a user's session.
Password Change: To invalidate all old tokens.
Role Changes: To force re-authentication with new permissions.

The Stateless Challenge

JWTs are inherently stateless. Once issued, they contain all necessary information for validation and don't require the server to store session data.

This statelessness is a strength, but it makes direct server-side revocation tricky. The server typically doesn't hold a list of active tokens to simply 'turn off'.

Blacklisting Explained

Blacklisting is a common strategy to revoke JWTs. When a token needs to be invalidated, its unique identifier (often the JTI claim) is added to a 'blacklist' — a list of forbidden tokens.

Any token whose JTI is on this list is rejected, even if it's cryptographically valid and not expired.
This allows you to 'undo' a token's validity.

Implementing a Blacklist

The blacklist needs to be stored in a highly available, fast-access data store. Speed is crucial because every incoming request might need to check this list.

Redis: An excellent choice due to its in-memory nature and support for time-to-live (TTL) on entries, which can match token expiry.
Database: A simple table can work, but might be slower for high-volume checks.
Each entry typically stores the JWT's JTI and its original expiry time.

Simple Blacklist Service

Here's a basic interface for a service that manages a token blacklist. In a real application, this would interact with a database or a caching system like Redis.

public interface TokenBlacklistService {
  void blacklistToken(String jti, long expirySeconds);
  boolean isBlacklisted(String jti);
}

JWT Filter with Blacklist Check

When a request arrives, a security filter would first validate the JWT's signature and expiry. Then, it would check if the token's JTI is present on the blacklist before granting access.

Try running this example:

import java.util.HashSet;
import java.util.Set;

// A simplified in-memory blacklist for demonstration
class MockTokenBlacklistService {
    private Set<String> blacklistedJtis = new HashSet<>();

    public void blacklistToken(String jti, long expirySeconds) {
        System.out.println("Action: Blacklisting JTI " + jti);
        blacklistedJtis.add(jti);
        // In a real app, 'expirySeconds' would set a TTL on the blacklist entry
    }

    public boolean isBlacklisted(String jti) {
        boolean result = blacklistedJtis.contains(jti);
        System.out.println("Check: Is JTI " + jti + " blacklisted? " + result);
        return result;
    }
}

public class Main {
    public static void main(String[] args) {
        MockTokenBlacklistService blacklist = new MockTokenBlacklistService();

        String userTokenJti = "user-abc-123";
        String adminTokenJti = "admin-def-456";

        // Simulate an admin token being revoked after a security event
        blacklist.blacklistToken(adminTokenJti, 3600); // Token expires in 1 hour

        // Check access for different tokens
        System.out.println("\n--- Access Checks ---");
        System.out.println("User token access: " + (blacklist.isBlacklisted(userTokenJti) ? "DENIED" : "GRANTED"));
        System.out.println("Admin token access: " + (blacklist.isBlacklisted(adminTokenJti) ? "DENIED" : "GRANTED"));
    }
}

Whitelisting Explained

Whitelisting is an alternative revocation strategy. Instead of listing forbidden tokens, you maintain a list of active, allowed tokens.

When a token is issued, its JTI is added to a 'whitelist'.
For every request, the token's JTI must be found on this whitelist to be considered valid.
If a token's JTI is not on the whitelist, it's rejected.

Implementing a Whitelist

Similar to blacklisting, a whitelist requires a fast, persistent store (e.g., Redis). The key difference is what you store and how you manage it:

Each entry typically stores the JWT's JTI, often associated with a user ID.
When a user logs out or changes their password, all active JTIs associated with that user can be efficiently removed from the whitelist.

Blacklist vs. Whitelist Comparison

Both strategies achieve revocation but have different implications:

Blacklist: Ideal for rare, specific revocations (e.g., single token compromise). Requires less storage if revocations are infrequent.
Whitelist: Better for frequent revocations (e.g., user logout invalidates all tokens). Can simplify session management but requires more storage for all active tokens.
The choice depends on your application's specific needs and the frequency of revocations.

Revocation Scenario

Consider an application where users frequently log out, and you need to ensure all their issued tokens are immediately invalidated upon logout.

Recap: Revocation Strategies

In this lesson, we've explored advanced strategies for revoking JWTs, which is crucial for robust security:

Blacklisting: Marking specific tokens as invalid by adding their JTI to a forbidden list.
Whitelisting: Only allowing tokens that are explicitly listed as active, often tied to a user session.
The best approach depends on your application's requirements, especially the frequency and nature of token invalidation.

Next, we'll analyze the performance implications of these techniques.

Frequently asked questions

Is the “JWT Blacklisting and Whitelisting” lesson free?

Yes — the full text of “JWT Blacklisting and Whitelisting” is free to read here on the web, and the Spring Security 6 & JWT Authentication course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Security 6 & JWT Authentication course, upgrade to CoddyKit PRO.

What will I learn in “JWT Blacklisting and Whitelisting”?

Deep dive into advanced token revocation techniques, including maintaining blacklists or whitelists of tokens. You practise Spring Security 6 & JWT Authentication with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Spring Security 6 & JWT Authentication?

No prior experience is required. Spring Security 6 & JWT Authentication on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “JWT Blacklisting and Whitelisting” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Spring Security 6 & JWT Authentication lesson?

Yes. Every Spring Security 6 & JWT Authentication lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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