How do you implement custom filters for JWT authentication?
Table of Contents
Introduction
JWT (JSON Web Tokens) is a widely used method for securing REST APIs, and implementing custom filters for JWT authentication is essential in a Spring Boot application. These filters intercept incoming HTTP requests, validate JWT tokens, and authenticate users before allowing access to protected resources.
In this guide, we'll go through the process of implementing a custom filter to validate JWT tokens in a Spring Boot application. This filter will be integrated into Spring Security to secure REST endpoints and ensure only authenticated users can access the protected resources.
Steps to Implement Custom Filters for JWT Authentication
1. Add Necessary Dependencies
To start, ensure that your Spring Boot project has the required dependencies for Spring Security and the jjwt
library for handling JWT tokens.
Here’s how you can include them in your pom.xml
:
2. Create JWT Utility Class
Create a utility class to handle the creation, parsing, and validation of JWT tokens. This class will be used by the custom filter to validate the tokens.
Example JwtUtil.java
:
In this utility class:
createJwt()
generates a signed JWT token.parseJwt()
decodes and retrieves the claims from the token.isTokenExpired()
checks whether the token has expired.
3. Create the JWT Filter
The core of the JWT authentication process is the filter. This custom filter will intercept incoming requests, extract the JWT token from the Authorization
header, and validate it. If the token is valid, the filter will authenticate the user.
Example JwtAuthenticationFilter.java
:
In this filter:
- We extract the JWT token from the
Authorization
header. - If the token is valid, we parse it and check if it is expired.
- If the token is valid, we create a custom authentication token (
JwtAuthenticationToken
) and set it in the Spring Security context. - If the token is invalid, we send an
Unauthorized
response.
4. Create the Custom Authentication Token
We need to create a custom authentication token class that holds the user’s information (such as the username) from the JWT. This class extends AbstractAuthenticationToken
to integrate with Spring Security.
Example JwtAuthenticationToken.java
:
5. Configure Spring Security to Use the JWT Filter
Once the filter is created, we need to configure Spring Security to add this filter to the security chain. This is done by modifying the SecurityConfig
class and adding the custom filter to the filter chain.
Example SecurityConfig.java
:
In this configuration:
- We disable CSRF (since we’re using stateless authentication).
- The
/login
endpoint is public, but all other endpoints are secured and require a valid JWT. - We add our custom
JwtAuthenticationFilter
to the Spring Security filter chain before other filters.
6. Create the Login Endpoint to Issue JWT
To issue JWT tokens, we need a login endpoint where users will authenticate and receive a token. For simplicity, we’ll assume the login is handled by username and password.
Example AuthController.java
:
In this controller:
- We provide a
/login
endpoint where users can submit their credentials to receive a JWT token.
Conclusion
By implementing a custom JWT authentication filter in Spring Boot, you ensure that all incoming requests are properly authenticated before accessing protected resources. The steps outlined include:
- Creating a utility class to handle JWT token creation, parsing, and validation.
- Building a custom filter to extract and validate JWT tokens from the
Authorization
header. - Configuring Spring Security to use the filter and secure the application’s endpoints.
This approach ensures your API is protected using JWT-based authentication, providing secure access to only authenticated users.