Spring Boot JWT

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File structure

spring-boot-jwt/
 │
 ├── src/main/java/
 │   └── murraco
 │       ├── configuration
 │       │   └── OpenApiConfig.java
 │       │
 │       ├── controller
 │       │   └── UserController.java
 │       │
 │       ├── dto
 │       │   ├── UserDataDTO.java
 │       │   └── UserResponseDTO.java
 │       │
 │       ├── exception
 │       │   ├── CustomException.java
 │       │   └── GlobalExceptionHandlerController.java
 │       │
 │       ├── model
 │       │   ├── AppUserRole.java
 │       │   └── AppUser.java
 │       │
 │       ├── repository
 │       │   └── UserRepository.java
 │       │
 │       ├── security
 │       │   ├── JwtTokenFilter.java
 │       │   ├── JwtTokenProvider.java
 │       │   ├── MyUserDetails.java
 │       │   └── WebSecurityConfig.java
 │       │
 │       ├── service
 │       │   └── UserService.java
 │       │
 │       └── JwtAuthServiceApp.java
 │
 ├── src/main/resources/
 │   ├── application.yml        # default profile (dev), JWT placeholders
 │   └── application-dev.yml    # H2, JPA, server.port, H2 console (dev)
 │
 ├── src/test/java/murraco/controller/
 │   └── UserControllerTest.java
 │
 ├── .gitignore
 ├── Dockerfile
 ├── LICENSE
 ├── mvnw, mvnw.cmd
 ├── README.md
 └── pom.xml

Architecture overview

This is a REST API with stateless JWT authentication. The endpoints /users/signin and /users/signup are public; all other endpoints require a valid JWT in the Authorization: Bearer <token> header. Roles ROLE_ADMIN and ROLE_CLIENT are enforced via @PreAuthorize on controller methods.

sequenceDiagram
  participant Client
  participant Filter as JwtTokenFilter
  participant Provider as JwtTokenProvider
  participant Controller
  participant Service

  Note over Client,Service: Signin (no token)
  Client->>Controller: POST /users/signin
  Controller->>Service: signin(username, password)
  Service->>Client: JWT token

  Note over Client,Service: Protected request
  Client->>Filter: GET /users/me + Bearer JWT
  Filter->>Provider: resolveToken, validateToken
  Provider->>Provider: getAuthentication (load user)
  Filter->>Controller: set SecurityContext, doFilter
  Controller->>Service: whoami(req)
  Service->>Client: UserResponseDTO

Loading

JWT flow in this project

1. Obtain a token: Send POST /users/signin with username and password (form or query params). The response is the JWT string.
2. Call protected APIs: Send the token in the header: Authorization: Bearer <token>.
3. Filter chain: JwtTokenFilter reads the header, validates the token via JwtTokenProvider, loads the user via MyUserDetails, and sets Spring’s SecurityContext.
4. Authorization: Controllers use @PreAuthorize("hasRole('ROLE_ADMIN')") (or similar) so only users with the right role can access the endpoint.

Core classes: JwtTokenFilter, JwtTokenProvider, MyUserDetails, WebSecurityConfig (SecurityFilterChain), and OpenApiConfig (SpringDoc).

Introduction (https://jwt.io)

Just to throw some background in, we have a wonderful introduction, courtesy of jwt.io! Let’s take a look:

What is JSON Web Token?

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with the HMAC algorithm) or a public/private key pair using RSA.

Let's explain some concepts of this definition further.

Compact: Because of their smaller size, JWTs can be sent through a URL, POST parameter, or inside an HTTP header. Additionally, the smaller size means transmission is fast.

Self-contained: The payload contains all the required information about the user, avoiding the need to query the database more than once.

When should you use JSON Web Tokens?

Here are some scenarios where JSON Web Tokens are useful:

Authentication: This is the most common scenario for using JWT. Once the user is logged in, each subsequent request will include the JWT, allowing the user to access routes, services, and resources that are permitted with that token. Single Sign On is a feature that widely uses JWT nowadays, because of its small overhead and its ability to be easily used across different domains.

Information Exchange: JSON Web Tokens are a good way of securely transmitting information between parties. Because JWTs can be signed—for example, using public/private key pairs—you can be sure the senders are who they say they are. Additionally, as the signature is calculated using the header and the payload, you can also verify that the content hasn't been tampered with.

What is the JSON Web Token structure?

JSON Web Tokens consist of three parts separated by dots (.), which are:

1. Header
2. Payload
3. Signature

Therefore, a JWT typically looks like the following.

xxxxx.yyyyy.zzzzz

Let's break down the different parts.

Header

The header typically consists of two parts: the type of the token, which is JWT, and the hashing algorithm being used, such as HMAC SHA256 or RSA.

For example:

{
  "alg": "HS256",
  "typ": "JWT"
}

Then, this JSON is Base64Url encoded to form the first part of the JWT.

Payload

The second part of the token is the payload, which contains the claims. Claims are statements about an entity (typically, the user) and additional metadata. There are three types of claims: reserved, public, and private claims.

• Reserved claims: These are a set of predefined claims which are not mandatory but recommended, to provide a set of useful, interoperable claims. Some of them are: iss (issuer), exp (expiration time), sub (subject), aud (audience), and others.

Notice that the claim names are only three characters long as JWT is meant to be compact.

• Public claims: These can be defined at will by those using JWTs. But to avoid collisions they should be defined in the IANA JSON Web Token Registry or be defined as a URI that contains a collision resistant namespace.

• Private claims: These are the custom claims created to share information between parties that agree on using them.

An example of payload could be:

{
  "sub": "1234567890",
  "name": "John Doe",
  "admin": true
}

The payload is then Base64Url encoded to form the second part of the JSON Web Token.

Signature

To create the signature part you have to take the encoded header, the encoded payload, a secret, the algorithm specified in the header, and sign that.

For example if you want to use the HMAC SHA256 algorithm, the signature will be created in the following way:

HMACSHA256(
  base64UrlEncode(header) + "." +
  base64UrlEncode(payload),
  secret)

The signature is used to verify that the sender of the JWT is who it says it is and to ensure that the message wasn't changed along the way. Putting all together

The output is three Base64 strings separated by dots that can be easily passed in HTML and HTTP environments, while being more compact when compared to XML-based standards such as SAML.

The following shows a JWT that has the previous header and payload encoded, and it is signed with a secret. Encoded JWT

How do JSON Web Tokens work?

In authentication, when the user successfully logs in using their credentials, a JSON Web Token will be returned and must be saved locally (typically in local storage, but cookies can be also used), instead of the traditional approach of creating a session in the server and returning a cookie.

Whenever the user wants to access a protected route or resource, the user agent should send the JWT, typically in the Authorization header using the Bearer schema. The content of the header should look like the following:

Authorization: Bearer <token>

This is a stateless authentication mechanism as the user state is never saved in server memory. The server's protected routes will check for a valid JWT in the Authorization header, and if it's present, the user will be allowed to access protected resources. As JWTs are self-contained, all the necessary information is there, reducing the need to query the database multiple times.

This allows you to fully rely on data APIs that are stateless and even make requests to downstream services. It doesn't matter which domains are serving your APIs, so Cross-Origin Resource Sharing (CORS) won't be an issue as it doesn't use cookies.

The following diagram shows this process:

JWT Authentication Summary

Token based authentication schema's became immensely popular in recent times, as they provide important benefits when compared to sessions/cookies:

• CORS
• No need for CSRF protection
• Better integration with mobile
• Reduced load on authorization server
• No need for distributed session store

Some trade-offs have to be made with this approach:

• More vulnerable to XSS attacks
• Access token can contain outdated authorization claims (e.g when some of the user privileges are revoked)
• Access tokens can grow in size in case of increased number of claims
• File download API can be tricky to implement
• True statelessness and revocation are mutually exclusive

JWT Authentication flow is very simple

1. User obtains Refresh and Access tokens by providing credentials to the Authorization server
2. User sends Access token with each request to access protected API resource
3. Access token is signed and contains user identity (e.g. user id) and authorization claims.

It's important to note that authorization claims will be included with the Access token. Why is this important? Well, let's say that authorization claims (e.g user privileges in the database) are changed during the life time of Access token. Those changes will not become effective until new Access token is issued. In most cases this is not big issue, because Access tokens are short-lived. Otherwise go with the opaque token pattern.

Implementation Details

Let's see how can we implement the JWT token based authentication using Java and Spring, while trying to reuse the Spring security default behavior where we can. The Spring Security framework comes with plug-in classes that already deal with authorization mechanisms such as: session cookies, HTTP Basic, and HTTP Digest. Nevertheless, it lacks from native support for JWT, and we need to get our hands dirty to make it work.

H2 DB

This demo uses an H2 in-memory database test_db when the dev profile is active (see application-dev.yml, merged with application.yml). The dev profile enables the H2 web console (spring.h2.console.enabled: true). Open http://localhost:8080/h2-console (JDBC URL jdbc:h2:mem:test_db, user root, password root as in the YAML). Spring Security permits /h2-console/** for local testing only—do not expose that in production.

If you want a different database, change the datasource in application-dev.yml (or a prod profile) instead of only application.yml. Note that ddl-auto: create-drop rebuilds the schema on each restart (change it for real deployments). Example settings (also reflected in application-dev.yml):

spring:
  h2:
    console:
      enabled: true
  datasource:
    url: jdbc:h2:mem:test_db;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE
    # url: jdbc:mysql://localhost:3306/user_db
    username: root
    password: root
  jpa:
    hibernate:
      ddl-auto: create-drop
    properties:
      hibernate:
        format_sql: true
        id:
          new_generator_mappings: false

Core Code

1. JwtTokenFilter
2. JwtTokenProvider (JJWT 0.12.x, HMAC-SHA256)
3. MyUserDetails
4. WebSecurityConfig (SecurityFilterChain, method security)
5. OpenApiConfig (SpringDoc OpenAPI 3)

JwtTokenFilter

The JwtTokenFilter filter is applied to each API (/**) with exception of the signin token endpoint (/users/signin) and signup endpoint (/users/signup).

This filter has the following responsibilities:

1. Check for access token in Authorization header. If Access token is found in the header, delegate authentication to JwtTokenProvider otherwise throw authentication exception
2. Invokes success or failure strategies based on the outcome of authentication process performed by JwtTokenProvider

Please ensure that chain.doFilter(request, response) is invoked upon successful authentication. You want processing of the request to advance to the next filter, because very last one filter FilterSecurityInterceptor#doFilter is responsible to actually invoke method in your controller that is handling requested API resource.

String token = jwtTokenProvider.resolveToken((HttpServletRequest) req);
if (token != null && jwtTokenProvider.validateToken(token)) {
  Authentication auth = jwtTokenProvider.getAuthentication(token);
  SecurityContextHolder.getContext().setAuthentication(auth);
}
filterChain.doFilter(req, res);

JwtTokenProvider

The JwtTokenProvider has the following responsibilities:

1. Verify the access token's signature
2. Extract identity and authorization claims from Access token and use them to create UserContext
3. If Access token is malformed, expired or simply if token is not signed with the appropriate signing key Authentication exception will be thrown

MyUserDetails

Implements UserDetailsService in order to define our own custom loadUserbyUsername function. The UserDetailsService interface is used to retrieve user-related data. It has one method named loadUserByUsername which finds a user entity based on the username and can be overridden to customize the process of finding the user.

It is used by the DaoAuthenticationProvider to load details about the user during authentication.

WebSecurityConfig

Defines a SecurityFilterChain bean (Spring Security 6): stateless sessions, CSRF disabled for the JWT API, authorizeHttpRequests with requestMatchers, JWT filter registered with addFilterBefore, and an AccessDeniedHandler for JSON-style 403 responses. AuthenticationManager is exposed as a bean for UserService#signin.

@Bean
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
  http.csrf(csrf -> csrf.disable());
  http.sessionManagement(sm -> sm.sessionCreationPolicy(SessionCreationPolicy.STATELESS));
  http.authorizeHttpRequests(auth -> auth
      .requestMatchers("/users/signin", "/users/signup").permitAll()
      .requestMatchers("/h2-console/**").permitAll()
      .requestMatchers("/v3/api-docs/**", "/swagger-ui/**", "/swagger-ui.html").permitAll()
      .anyRequest().authenticated());
  http.exceptionHandling(ex -> ex.accessDeniedHandler((request, response, exn) ->
      response.sendError(HttpServletResponse.SC_FORBIDDEN, "Access denied")));
  http.addFilterBefore(new JwtTokenFilter(jwtTokenProvider), UsernamePasswordAuthenticationFilter.class);
  http.headers(headers -> headers.frameOptions(frame -> frame.sameOrigin()));
  return http.build();
}

How to use this code?

Configuration

For production, set the JWT secret via environment variables. The default secret-key in application.yml is for local development only and must not be used in production.

Variable	Description	Default
JWT_SECRET	Secret key used to sign JWT tokens. Use a long, random value (e.g. 256+ bits).	secret-key (dev only)
JWT_EXPIRE_MS	Token validity in milliseconds.	300000 (5 minutes)

Example: export JWT_SECRET=your-secure-random-secret before running the application.

Production: Disable or protect the H2 console and use a real database (e.g. MySQL). The in-memory H2 and open /h2-console/** are for development only.

Profiles: The default profile is dev (see application-dev.yml for H2 and server settings). For production, set spring.profiles.active=prod and configure JWT_SECRET, database URL, and disable H2 console as needed.

Quick start: After running the app, two demo users exist (created idempotently on startup if missing): admin / admin123456 and client / client123456 (passwords meet validation @Size(min = 8)). With profile dev, the app uses in-memory H2 (see application-dev.yml); the schema is recreated on each restart. For MySQL, switch the datasource in application-dev.yml (or your prod profile). The H2 console is enabled only in that dev configuration.

Docker: Build and run with docker build -t spring-boot-jwt . then docker run -p 8080:8080 spring-boot-jwt. For production, pass -e JWT_SECRET=your-secret.

Setup

1. Install JDK 17 or newer (LTS recommended, e.g. Temurin 17 or 21) and Maven 3.6.3+, or use the included ./mvnw wrapper

2. Fork this repository and clone it

$ git clone https://github.com/<your-user>/spring-boot-jwt

3. Navigate into the folder

$ cd spring-boot-jwt

4. Install dependencies

$ mvn install

5. Run the project

$ mvn spring-boot:run

6. Open Swagger UI (SpringDoc): http://localhost:8080/swagger-ui.html (redirects to /swagger-ui/index.html). OpenAPI JSON: http://localhost:8080/v3/api-docs. Click Authorize, select scheme bearerAuth, and enter Bearer <your_jwt>. Default port is 8080 (application-dev.yml).

server:
  port: 8080

7. Make a GET request to /users/me to check you're not authenticated. You should receive a response with a 403 with an Access Denied message since you haven't set your valid JWT token yet

$ curl -X GET http://localhost:8080/users/me

8. Make a POST request to /users/signin with the default admin user we programmatically created to get a valid JWT token

$ curl -X POST 'http://localhost:8080/users/signin?username=admin&password=admin123456'

To sign up a new user (returns a JWT):

$ curl -X POST http://localhost:8080/users/signup -H "Content-Type: application/json" -d '{"username":"newuser","email":"new@example.com","password":"password8","appUserRoles":["ROLE_CLIENT"]}'

9. Add the JWT token as a Header parameter and make the initial GET request to /users/me again

$ curl -X GET http://localhost:8080/users/me -H 'Authorization: Bearer <JWT_TOKEN>'

10. And that's it, congrats! You should get a similar response to this one, meaning that you're now authenticated

{
  "id": 1,
  "username": "admin",
  "email": "admin@email.com",
  "appUserRoles": [
    "ROLE_ADMIN"
  ]
}

Testing

Run the suite with:

./mvnw test

Integration-style tests use @SpringBootTest + MockMvc. For environments where the Mockito inline mock maker cannot attach to the JVM, the project uses the subclass mock maker via src/test/resources/mockito-extensions/org.mockito.plugins.MockMaker.

Version notes

This project targets Spring Boot 3.5.x (LTS line; see spring-boot-starter-parent version in pom.xml), Java 17+, Spring Security 6 (SecurityFilterChain, authorizeHttpRequests), Jakarta EE namespaces (jakarta.*), JJWT 0.12.x, and SpringDoc OpenAPI (replacing Springfox).

Migration from Spring Boot 2.x

If you are upgrading an older fork: replace javax.* with jakarta.*, migrate security configuration to SecurityFilterChain, swap Springfox for SpringDoc, upgrade JWT libraries to JJWT 0.12+, and run on JDK 17+. See the Spring Boot 3.0 migration guide and Spring Security 6.0 migration.

Contribution

• Report issues
• Open pull request with improvements
• Spread the word
• Reach out to me directly at mauriurraco@gmail.com

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