Spring Method Level Security with Amazon Cognito and JWT Token
Tags: java, spring, cognito, aws
Published: 2022-10-24 02:13:33

Learn how to authenticate your user with AWS Cognito and secure your Spring REST endpoints with JWT token at the method level using Spring Security.

## 1. Introduction
The goal of this tutorial is to authenticate and authorize a user in a Spring REST service using the JWT token.

### 1.1 Prerequisite

- Create a user pool in Amazon Cognito.
- Create an application in Google Console.
  - Add a user/email that we can authenticate later for testing.

Follow this guide  [Next with AWS Cognito](https://www.czetsuyatech.com/2021/06/nextjs-security-with-aws-cognito.html) in case you are not familiar with them.

### 1.2 Goal - Create a Java Library with the following Features

- Decoding an AWS Cognito JWT token.
- Verifying the JWT token issuer.
- Creating a custom SimpleCtAccount using the information contained in the JWT token.
- Convert the associated Cognito groups into a custom CtRole.
- A single interface to enable security.

## 2. The Spring Security Module
Spring has provided a lot of utility classes that we can use to secure our web application. One such class that we will use in our library is the WebSecurityConfigurerAdapter class to customize our HTTP and Web Security.

## 3. Class Diagram

### 3.1 Method Security
What if we wanted to do a finely detailed check on a particular method? For example, is this user living in the Philippines? Or is this user a member of a particular group? 

This is where the Spring class  GlobalMethodSecurityConfiguration comes in. First, let's take a look at the class diagram.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/d1c2h0n5pk01re5howw0.png)

In this diagram, most of the common authorization checks are defined in  CtMethodSecurityExpressionRoot. This class is extended by  DefaultMethodSecurityExpressionRoot which we can extend on our microservice to provide additional authorization checks (This will be covered later).

To inform Spring and pickup this configuration, we need to annotate the class CtMethodSecurityConfiguration with: @Configuration and @EnableGlobalMethodSecurity(prePostEnabled = true).

## 4. How to use our Library?

### 4.1 Service Integration
I have uploaded this library on maven central for convenience. Also, the source code is 100% open-source on GitHub.

To use on a project:
1. Add a maven dependency:

```
<dependency>
    <groupId>com.czetsuyatech</groupId>
    <artifactId>ct-iam-spring-security</artifactId>
    <version>LATEST-SNAPSHOT</version>
</dependency>
```

2. Extend the class  DefaultMethodSecurityExpressionRoot, and add more authorization checks.

```
public class CtAppMethodSecurityExpressionExtension extends DefaultMethodSecurityExpressionRoot {
 
  public CtAppMethodSecurityExpressionExtension(Authentication authentication) {
    super(authentication);
  }
 
  public boolean isAuthorized() {
    return true;
  }
 
  public boolean isUnAuthorized() {
    return false;
  }
}
```

3. Create a Configuration class  CtAppSecurityConfiguration where we will initialize the HTTP security and produce the  CtMethodSecurityExpressionHandler bean.

```
@Configuration
@RequiredArgsConstructor
@EnableCtSecurity
public class CtAppSecurityConfiguration {
 
  @Bean
  public CtHttpSecurityConfigurer httpSecurityConfig() {
 
    return http ->
        http
            .authorizeHttpRequests(authz -> authz
                .antMatchers(HttpMethod.GET, "/actuator/**").permitAll()
                .antMatchers("/api/**").authenticated()
                .anyRequest().permitAll()
            );
  }
 
  @Bean
  public CtMethodSecurityExpressionHandlerFactory methodSecurityFactory() {
    return CtAppMethodSecurityExpressionRoot::new;
  }
}
```

Don't forget to annotate this class with @EnableCtSecurity.

### 4.2 Secured Endpoints
Create a new controller with the following endpoints and use the @PreAuthorize annotation.

```
@RestController
@Validated
@Slf4j
@RequiredArgsConstructor
public class ApiTestController {
 
  @GetMapping("/hello")
  @ResponseStatus(HttpStatus.OK)
  public String hello(@CurrentSecurityContext(expression = "authentication") Authentication auth) {
 
    log.debug("" + auth.getPrincipal());
    log.debug("" + auth.getCredentials());
    log.debug("" + auth.getDetails());
 
    return "Hello " + auth.getPrincipal();
  }
 
  @GetMapping("/api/testing/authenticated")
  @PreAuthorize("isAuthenticated()")
  @ResponseStatus(HttpStatus.OK)
  public String authenticated(@CurrentSecurityContext(expression = "authentication") Authentication auth) {
 
    log.debug("" + auth.getPrincipal());
    log.debug("" + auth.getCredentials());
    log.debug("" + auth.getDetails());
 
    return "Hello " + auth.getPrincipal();
  }
 
  @GetMapping("/api/testing/authorized")
  @PreAuthorize("isAuthorized()")
  @ResponseStatus(HttpStatus.OK)
  public String authorized() {
    return "authorized";
  }
 
  @GetMapping("/api/testing/unauthorized")
  @PreAuthorize("isUnAuthorized()")
  @ResponseStatus(HttpStatus.FORBIDDEN)
  public String unAuthorized() {
    return "unauthorized";
  }
}
```

## 5. References

- https://www.czetsuyatech.com/2021/01/aws-generate-cognito-access-token.html
- https://github.com/czetsuyatech/ct-iam-spring-security (GitHub sponsors only)
- https://github.com/czetsuyatech/ct-aws-cognito-spring-security