Interceptors in Spring Boot

Interceptors in Spring Boot

Interceptors are a powerful mechanism in Spring Boot that allow you to intercept incoming HTTP requests and responses at various stages of their processing. This enables you to perform common tasks like:

1.Authentication and Authorization: Validate user credentials and access permissions before processing requests.

2.Logging and Monitoring: Capture request and response details for debugging and performance analysis.

3.Request/Response Transformation: Modify request headers or body content, or manipulate response data before sending it back to the client.

4.Cross-Cutting Concerns: Implement functionality that applies across multiple controllers in your application.

Implementing an Interceptor

To create an Interceptor, you typically follow these steps:

1.Create a Class: Define a class that implements the HandlerInterceptor interface or extends the HandlerInterceptorAdapter class.

2.Override Methods: Implement the following methods (at least one is required):

• preHandle(HttpServletRequest, HttpServletResponse, Object): Invoked before the controller method is executed. Return true to allow the request to proceed, or false to block it.
• postHandle(HttpServletRequest, HttpServletResponse, Object, ModelAndView) (optional): Invoked after the controller method has been executed, but before the response is sent.
• afterCompletion(HttpServletRequest, HttpServletResponse, Object, Exception) (optional): Invoked after the request has been fully processed, regardless of whether an exception occurred.

OAuth Example with Interceptor

Here’s a detailed example of using an Interceptor for OAuth authentication in a Spring Boot application:

1. Dependencies:

Make sure you have the necessary dependencies for Spring Security OAuth2.

<dependency>    <groupId>org.springframework.boot</groupId>    <artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>    <groupId>org.springframework.security</groupId>    <artifactId>spring-security-oauth2-client</artifactId>
</dependency>

2. Security Configuration:

Configure Spring Security to use OAuth2 client credentials grant:

@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/api/public").permitAll() // Allow public API access
                .anyRequest().authenticated()
            .and()
                .oauth2Login()
                .clientCredentials() // Use client credentials grant
                    .clientId("your-client-id")
                    .clientSecret("your-client-secret");
    }
}

3. OAuth Interceptor:

Create an Interceptor that checks for a valid access token in the request header:

@Component
public class OAuthInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String authorization = request.getHeader("Authorization");
        if (authorization == null || !authorization.startsWith("Bearer ")) {
            response.sendError(HttpStatus.UNAUTHORIZED.value(), "Missing or invalid access token");
            return false;
        }

        String token = authorization.substring(7); // Extract token after "Bearer "

        // Implement logic to validate the token (e.g., using a Token Introspection endpoint)
        // ... (replace with your token validation logic)

        return true; // Allow request to proceed if token is valid
    }
}

4. Registering the Interceptor:

In your Spring Boot application configuration (e.g., @SpringBootApplication class), register the Interceptor with Spring MVC:

@SpringBootApplication
public class YourApplication {

    public static void main(String[] args) {
        SpringApplication.run(YourApplication.class, args);
    }

    @Bean
    public WebMvcConfigurerAdapter webMvcConfigurerAdapter() {
        return new WebMvcConfigurerAdapter() {
            @Override
            public void addInterceptors(InterceptorRegistry registry) {
                registry.addInterceptor(new OAuthInterceptor());
            }
        };
    }
}

Explanation:

• This example uses the client credentials grant, which is suitable for machine-to-machine authentication.
• The Interceptor checks for the presence of an Authorization header with a Bearer token.
• You’ll need to replace the placeholder token validation logic with your actual implementation, which could involve contacting a token introspection endpoint to verify the token’s validity.
• If the token is valid, the request proceeds. Otherwise not.

Happy Learning,