Welcome back! In the previous lessons, you learned how to generate secure API keys, store them safely, and use them to authenticate requests to your Spring Boot application. You also saw how to combine API key authentication with JWTs for flexible access control. Now that you have a solid foundation in creating and authenticating API keys, it is time to focus on managing them securely.

In this lesson, you will learn how to list your API keys in a way that protects sensitive information, how to revoke (deactivate) keys when they are no longer needed, and how to protect your API from abuse using rate limiting. These are essential skills for any real-world API, as they help you maintain security, support auditing, and prevent misuse. By the end of this lesson, you will be able to build robust API key management endpoints and understand how to integrate them into your Spring Boot application.

When building an API key management system, it is important to allow users to view their keys — but you must never expose the full API key after it is created. This is a key security principle: if someone gains access to the list of keys, they should not be able to use them directly.

Let's look at how you can implement a secure listing endpoint. In the example below, the /api/api-keys/list route retrieves all API keys for the authenticated user. Instead of returning the full key, it provides a preview (just the prefix and asterisks), along with metadata such as the key's name, status, and expiration date.

In this code, the endpoint first fetches all API keys for the current user using the JPA repository method findByUserIdOrderByCreatedAtDesc(). This is a Spring Data JPA derived query method — Spring automatically generates the implementation based on the method name. The findByUserId part tells Spring to filter by the field, sorts the results, specifies which field to sort by, and means descending order (newest first). So this method returns all keys for the user, sorted from most recent to oldest.

Sometimes, you need to disable an API key — maybe it was leaked, or it is no longer needed. Instead of deleting the key from the database, it is best practice to deactivate it. This keeps an audit trail, which is important for security and compliance. Deactivated keys can no longer be used, but you still have a record of their existence and history.

Here is how you can implement a revocation endpoint:

In this code, the endpoint looks up the API key by its ID and the current user using the JPA repository. If the key is found, it sets isActive to false and saves the change to the database. The action is logged for auditing. The response confirms the revocation and includes the key's ID and name.

A typical response would be:

By deactivating rather than deleting, you ensure that you can always review which keys existed and when they were revoked.

As your API grows, it is important to protect it from abuse. One common attack is to flood your API with requests, which can slow down or even crash your service. Rate limiting helps prevent this by restricting how many requests a user or API key can make in a given time period.

In Java/Spring Boot applications, you can use the Bucket4j library to implement rate limiting. In this example, you configure rate limiting to allow each API key 100 requests per hour. The filter checks if the request is authenticated with an API key and applies the limit accordingly. JWT and unauthenticated requests skip rate limiting entirely, as they typically represent interactive users who are less likely to abuse the API.

Here's how to implement the rate limiting filter:

Now that you have endpoints for listing and revoking API keys, and a rate limiting setup, you need to integrate them into your main Spring Boot application. This ensures that all API routes are protected and that key management is available to authenticated users.

Here is how the controller and filters are set up:

The rate limiting filter integrates automatically through Spring Boot's filter chain. Register the filter by adding a annotation to the class, and Spring Boot will automatically apply it to all requests. The filter checks the and attributes that should be set by an authentication filter earlier in the chain.

In this lesson, you learned how to manage API keys securely in your Spring Boot application. You saw how to list API keys without exposing sensitive information, how to revoke keys safely for audit purposes, and how to protect your API from abuse using rate limiting that specifically targets API key requests while allowing interactive users unrestricted access. You also learned how to integrate these features into your main Spring Boot application for a clean and secure architecture.

These skills are essential for any API that uses key-based authentication. They help you keep your users safe, support compliance, and maintain the reliability of your service. In the next set of practice exercises, you will get hands-on experience with these concepts, reinforcing what you have learned and preparing you to build secure, production-ready APIs. Remember, on CodeSignal, all the necessary libraries are pre-installed, so you can focus on writing and testing your code. Good luck, and keep building your security skills!