Course – LSS – NPI (cat=Spring Security)
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1. Overview

Adding custom claims to JSON Web Token (JWT) access tokens can be crucial in many scenarios. Custom claims allow us to include additional information in the token payload.

In this tutorial, we’ll learn how to add resource owner authorities to a JWT access token in the Spring Authorization Server.

2. Spring Authorization Server

The Spring Authorization Server is a new project in the Spring ecosystem designed to provide Authorization Server support to Spring applications. It aims to simplify the process of implementing OAuth 2.0 and OpenID Connect (OIDC) authorization servers using the familiar and flexible Spring programming model.

2.1. Maven Dependencies

Let’s start by importing the spring-boot-starter-web, spring-boot-starter-security, spring-boot-starter-test, and spring-security-oauth2-authorization-server dependencies to the pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <version>2.5.4</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
    <version>2.5.4</version>
</dependency>
<dependency>
    <groupId>org.springframework.security</groupId>
    <artifactId>spring-security-oauth2-authorization-server</artifactId>
    <version>0.2.0</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <version>2.5.4</version>
</dependency>

Alternatively, we can add the spring-boot-starter-oauth2-authorization-server dependency to our pom.xml file:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-oauth2-authorization-server</artifactId>
    <version>3.2.0</version>
</dependency>

2.2. Project Setup

Let’s set up the Spring Authorization Server for issuing access tokens. To keep things simple, we’ll be using the Spring Security OAuth Authorization Server application.

Let’s assume that we’re using the authorization server project available on GitHub.

3. Add Basic Custom Claims to JWT Access Tokens

In a Spring Security OAuth2-based application, we can add custom claims to JWT access tokens by customizing the token creation process in the Authorization Server. This type of claim can be useful for injecting additional information into JWTs, which can then be used by resource servers or other components in the authentication and authorization flow.

3.1. Add Basic Custom Claims

We can add our custom claims to an access token using the OAuth2TokenCustomizer<JWTEncodingContext> bean. By using it, every access token that is issued by the authorization server will have the custom claims populated.

Let’s add the OAuth2TokenCustomizer bean in the DefaultSecurityConfig class:

@Bean
@Profile("basic-claim")
public OAuth2TokenCustomizer<JwtEncodingContext> jwtTokenCustomizer() {
    return (context) -> {
      if (OAuth2TokenType.ACCESS_TOKEN.equals(context.getTokenType())) {
        context.getClaims().claims((claims) -> {
          claims.put("claim-1", "value-1");
          claims.put("claim-2", "value-2");
        });
      }
    };
}

The OAuth2TokenCustomizer interface is part of the Spring Security OAuth2 library and is used to customize OAuth 2.0 tokens. In this case, it specifically customizes JWT tokens during the encoding process. 

The lambda expression passed to the jwtTokenCustomizer() bean defines the customization logic. The context parameter represents the JwtEncodingContext during the token encoding process. 

First, we use the context.getTokenType() method to check whether the token being processed is an access token. Then, we obtain the claims associated with the JWT being constructed by using the context.getClaims() method. Finally, we add custom claims to the JWT.

In this example, two claims (“claim-1” and “claim-2“) with corresponding values (“value-1” and “value-2“) are added.

3.2. Test the Custom Claims

For testing, we are going to use the client_credentials grant type. 

First, we’ll define the client_credentials grant type from AuthorizationServerConfig as an authorized grant type in the RegisteredClient object:

@Bean
public RegisteredClientRepository registeredClientRepository() {
    RegisteredClient registeredClient = RegisteredClient.withId(UUID.randomUUID().toString())
      .clientId("articles-client")
      .clientSecret("{noop}secret")
      .clientAuthenticationMethod(ClientAuthenticationMethod.CLIENT_SECRET_BASIC)
      .authorizationGrantType(AuthorizationGrantType.CLIENT_CREDENTIALS)
      .authorizationGrantType(AuthorizationGrantType.AUTHORIZATION_CODE)
      .authorizationGrantType(AuthorizationGrantType.REFRESH_TOKEN)
      .redirectUri("http://127.0.0.1:8080/login/oauth2/code/articles-client-oidc")
      .redirectUri("http://127.0.0.1:8080/authorized")
      .scope(OidcScopes.OPENID)
      .scope("articles.read")
      .build();

    return new InMemoryRegisteredClientRepository(registeredClient);
}

Then, let’s create a test case in the CustomClaimsConfigurationTest class:

@ActiveProfiles(value = "basic-claim")
public class CustomClaimsConfigurationTest {

    private static final String ISSUER_URL = "http://localhost:";
    private static final String USERNAME = "articles-client";
    private static final String PASSWORD = "secret";
    private static final String GRANT_TYPE = "client_credentials";

    @Autowired
    private TestRestTemplate restTemplate;

    @LocalServerPort
    private int serverPort;

    @Test
    public void givenAccessToken_whenGetCustomClaim_thenSuccess() throws ParseException {
        String url = ISSUER_URL + serverPort + "/oauth2/token";
        HttpHeaders headers = new HttpHeaders();
        headers.setBasicAuth(USERNAME, PASSWORD);
        MultiValueMap<String, String> params = new LinkedMultiValueMap<>();
        params.add("grant_type", GRANT_TYPE);
        HttpEntity<MultiValueMap<String, String>> requestEntity = new HttpEntity<>(params, headers);
        ResponseEntity<TokenDTO> response = restTemplate.exchange(url, HttpMethod.POST, requestEntity, TokenDTO.class);

        SignedJWT signedJWT = SignedJWT.parse(response.getBody().getAccessToken());
        JWTClaimsSet claimsSet = signedJWT.getJWTClaimsSet();
        Map<String, Object> claims = claimsSet.getClaims();

        assertEquals("value-1", claims.get("claim-1"));
        assertEquals("value-2", claims.get("claim-2"));
    } 
    
    static class TokenDTO {
        @JsonProperty("access_token")
        private String accessToken;
        @JsonProperty("token_type")
        private String tokenType;
        @JsonProperty("expires_in")
        private String expiresIn;
        @JsonProperty("scope")
        private String scope;

        public String getAccessToken() {
            return accessToken;
        }
    }
}

Let’s walk through the key parts of our test to understand what is going on:

  • Start by constructing a URL for the OAuth2 token endpoint.
  • Retrieve a response containing the TokenDTO class from a POST request to the token endpoint. Here, we create an HTTP request entity with headers (basic authentication) and parameters (grant type).
  • Parse the Access Token from the response using the SignedJWT class. Also, we extract claims from the JWT and store them in the Map<String, Object>.
  • Assert that specific claims in the JWT have expected values using JUnit assertions.

This test confirms that our token encoding process is working properly and our claims are being generated as expected. Awesome!

In addition, we can get the access token using the curl command: 

curl --request POST \
  --url http://localhost:9000/oauth2/token \
  --header 'Authorization: Basic YXJ0aWNsZXMtY2xpZW50OnNlY3JldA==' \
  --header 'Content-Type: application/x-www-form-urlencoded' \
  --data grant_type=client_credentials

Here, the credentials are encoded as a Base64 string of the client ID and client secret, delimited by a single colon “:”.

Now, we can run our Spring Boot application with the profile basic-claim.

If we obtain an access token and decode it using jwt.io, we find the test claims in the token’s body:

{
  "sub": "articles-client",
  "aud": "articles-client",
  "nbf": 1704517985,
  "scope": [
    "articles.read",
    "openid"
  ],
  "iss": "http://auth-server:9000",
  "exp": 1704518285,
  "claim-1": "value-1",
  "iat": 1704517985,
  "claim-2": "value-2"
}

As we can see, the value of the test claims is as expected.

We’ll discuss adding authority as claims to access tokens in the following section.

4. Add Authorities as Custom Claims to JWT Access Tokens

Adding authorities as custom claims to JWT access tokens is often a crucial aspect of securing and managing access in a Spring Boot application. Authorities, typically represented by GrantedAuthority objects in Spring Security, indicate what actions or roles a user is allowed to perform. By including these authorities as custom claims in JWT access tokens, we provide a convenient and standardized way for resource servers to understand the user’s permissions.

4.1. Add Authorities as Custom Claims

First, we use a simple in-memory user configuration with a set of authorities in the DefaultSecurityConfig class:

@Bean
UserDetailsService users() {
    UserDetails user = User.withDefaultPasswordEncoder()
      .username("admin")
      .password("password")
      .roles("USER")
      .build();
    return new InMemoryUserDetailsManager(user);
}

A single user with the username “admin” password “password” and role “USER” is created.

Now, let’s populate a custom claim in the access token with those authorities:

@Bean
@Profile("authority-claim")
public OAuth2TokenCustomizer<JwtEncodingContext> tokenCustomizer(@Qualifier("users") UserDetailsService userDetailsService) {
    return (context) -> {
      UserDetails userDetails = userDetailsService.loadUserByUsername(context.getPrincipal().getName());
      Collection<? extends GrantedAuthority> authorities = userDetails.getAuthorities();
      context.getClaims().claims(claims ->
         claims.put("authorities", authorities.stream().map(authority -> authority.getAuthority()).collect(Collectors.toList())));
    };
}

First, we define a lambda function that implements the OAuth2TokenCustomizer<JwtEncodingContext> interface. This function customizes the JWT during the encoding process.

Then, we retrieve the UserDetails object associated with the current principal (user) from the injected UserDetailsService. The principal’s name is typically the username.

After that, we retrieve the collection of GrantedAuthority objects associated with the user. 

Finally, we retrieve the JWT claims from the JwtEncodingContext and apply customizations. It includes adding a custom claim named “authorities” to the JWT. Also, this claim contains a list of authority strings obtained from the GrantedAuthority objects associated with the user. 

4.2. Test the Authorities Claims

Now that we’ve configured the authorization server, let’s test it. For that, we’ll use the client-server project available on GitHub.

Let’s create a REST API client that will fetch the list of claims from the access token:

@GetMapping(value = "/claims")
public String getClaims(
  @RegisteredOAuth2AuthorizedClient("articles-client-authorization-code") OAuth2AuthorizedClient authorizedClient
) throws ParseException {
    SignedJWT signedJWT = SignedJWT.parse(authorizedClient.getAccessToken().getTokenValue());
    JWTClaimsSet claimsSet = signedJWT.getJWTClaimsSet();
    Map<String, Object> claims = claimsSet.getClaims();
    return claims.get("authorities").toString();
}

The @RegisteredOAuth2AuthorizedClient annotation is used in a Spring Boot controller method to indicate that the method expects an OAuth 2.0 authorized client to be registered with the specified client ID. In this case, the client ID is “articles-client-authorization-code“.

Let’s run our Spring Boot application with the profile authority-claim.

Now when we go into the browser and try to access the http://127.0.0.1:8080/claims page, we’ll be automatically redirected to the OAuth server login page under http://auth-server:9000/login URL.

After providing the proper username and password, the authorization server will redirect us back to the requested URL, the list of claims.

5. Conclusion

Overall, the ability to add custom claims to JWT access tokens provides a powerful mechanism for tailoring tokens to the specific needs of our application and enhancing the overall security and functionality of our authentication and authorization system.

In this article, we learned how to add custom claims and user authorities to a JWT access token in the Spring Authorization Server.

As always, the full source code is available over on GitHub.

Course – LSS (cat=Security/Spring Security)
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I just announced the new Learn Spring Security course, including the full material focused on the new OAuth2 stack in Spring Security:

>> CHECK OUT THE COURSE

res – Security (video) (cat=Security/Spring Security)
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