Last updated: 2023-02-06

Securing a REST API with Spring Security and JWT

Spring Security is the de facto standard for securing Spring Boot applications. JSON Web Token (JWT) is a good choice for protecting a REST API - the following article will show the minimal steps to setup a Spring Boot application with JWT.

The concept of JWT

As a first step, a client must authenticate itself using a username and password, receiving a signed token (JWT) in exchange. This token is stored locally at the client and is passed to the server with every further request, typically in the header. Since the token is signed using a key that only the server knows, the token and thus the client can be validated safely.

This approach makes the whole process stateless and very suitable for REST APIs, since no data about the state of the client (e.g. a session) needs to be stored. The username and the expiration date of the token are stored in the payload.

Example Payload of a JSON Web Token

Authentication endpoint

Spring Security does not provide direct support for JWT, so a number of additions to our Spring Boot application are necessary. In our build.gradle or pom.xml, we need to add the following two dependencies. Using the java-jwt library, we will later generate and validate the tokens.

Adding new dependencies

The following controller defines the first step from a client's perspective: an endpoint for authentication to obtain a valid token. To keep the code snippet short, the constructor with the field assignments is omitted.

@RestController
public class AuthenticationResource {

// ...

@PostMapping("/authenticate")
    public AuthenticationResponse authenticate(@RequestBody @Valid final AuthenticationRequest authenticationRequest) {
        try {
            authenticationManager.authenticate(new UsernamePasswordAuthenticationToken(
                    authenticationRequest.getLogin(), authenticationRequest.getPassword()));
        } catch (final BadCredentialsException ex) {
            throw new ResponseStatusException(HttpStatus.UNAUTHORIZED);
        }

final UserDetails userDetails = jwtUserDetailsService.loadUserByUsername(authenticationRequest.getLogin());
        final AuthenticationResponse authenticationResponse = new AuthenticationResponse();
        authenticationResponse.setAccessToken(jwtTokenService.generateToken(userDetails));
        return authenticationResponse;
    }

}

public class AuthenticationRequest {

@NotNull
    @Size(max = 255)
    private String login;

@NotNull
    @Size(max = 255)
    private String password;

}

public class AuthenticationResponse {

private String accessToken;

}

Authentication endpoint defined in our RestController

The request is validated and then passed to the authenticationManager for authentication. If successful, the JSON web token is generated and returned. There are no further details in the response, since the token itself should contain all relevant information.

Custom services

As referenced in our controller, the JwtTokenService is responsible for generating and validating the token. We store the secret used for these tasks in our application.properties or application.yml under the key jwt.secret. Make sure the key is at least 512 bits long, as this is required for this algorithm.

@Service
public class JwtTokenService {

private static final Duration JWT_TOKEN_VALIDITY = Duration.ofMinutes(20);

private final Algorithm hmac512;
    private final JWTVerifier verifier;

public JwtTokenService(@Value("${jwt.secret}") final String secret) {
        this.hmac512 = Algorithm.HMAC512(secret);
        this.verifier = JWT.require(this.hmac512).build();
    }

public String generateToken(final UserDetails userDetails) {
        final Instant now = Instant.now();
        return JWT.create()
                .withSubject(userDetails.getUsername())
                .withIssuer("app")
                .withIssuedAt(now)
                .withExpiresAt(now.plusMillis(JWT_TOKEN_VALIDITY.toMillis()))
                .sign(this.hmac512);
    }

public String validateTokenAndGetUsername(final String token) {
        try {
            return verifier.verify(token).getSubject();
        } catch (final JWTVerificationException verificationEx) {
            log.warn("token invalid: {}", verificationEx.getMessage());
            return null;
        }
    }

}

JwtTokenService encapsulating token handling

We also provide an implementation of the UserDetailsService that is accessed by the AuthenticationManager - which we configure later on. We access a table client using the ClientRepository, but any other source can be used here. We only assign the role ROLE_USER by default, although different roles and permissions could be used at this point as well.

Implementation of UserDetailsService

We're also using our own implementation of the UserDetails interface by extending the Spring Security org.springframework.security.core.userdetails.User class. While this is not strictly needed, it allows us to keep the primary key within the authentication details.

Extension of UserDetails

Authentication of the requests

To authenticate the requests going to our REST API, we need to define JwtRequestFilter. This filter ensures that a valid token is passed in the header and will store the UserDetails in the SecurityContext for the duration of the request.

@Component
public class JwtRequestFilter extends OncePerRequestFilter {

// ...

@Override
    protected void doFilterInternal(final HttpServletRequest request, final HttpServletResponse response,
                                    final FilterChain chain) throws ServletException, IOException {
        // look for Bearer auth header
        final String header = request.getHeader(HttpHeaders.AUTHORIZATION);
        if (header == null || !header.startsWith("Bearer ")) {
            chain.doFilter(request, response);
            return;
        }

final String token = header.substring(7);
        final String username = jwtTokenService.validateTokenAndGetUsername(token);
        if (username == null) {
            // validation failed or token expired
            chain.doFilter(request, response);
            return;
        }

// set user details on spring security context
        final JwtUserDetails userDetails = jwtUserDetailsService.loadUserByUsername(username);
        final UsernamePasswordAuthenticationToken authentication = new UsernamePasswordAuthenticationToken(
                userDetails, null, userDetails.getAuthorities());
        authentication.setDetails(new WebAuthenticationDetailsSource().buildDetails(request));
        SecurityContextHolder.getContext().setAuthentication(authentication);

// continue with authenticated user
        chain.doFilter(request, response);
    }

}

JwtRequestFilter to validate tokens

The following header must be present at the request so that our filter can validate the JWT and authenticate the request.

Example JWT submitted as a header

There is also the possibility to use the BearerTokenAuthenticationFilter of the library spring-boot-starter-oauth2-resource-server. However using our own filter gives us more flexibility and the user is loaded with its current data and roles from the JwtUserDetailsService on every request.

Spring Security config

This leads us to the heart of the matter, the configuration of Spring Security, which brings together all the previous components. With the current Spring Boot version 3.0.5 we should return the SecurityFilterChain and don't use the WebSecurityConfigurerAdapter anymore. Also, authorizeHttpRequests() and requestMatchers() are the favored methods right now.

Spring Security Configuration

The JwtUserDetailsService is to be used by the AuthenticationManager, along with a PasswordEncoder based on BCrypt. The PasswordEncoder is exposed as a bean, so it can be used at other parts of our application as well, for example when registering a user and creating the hash from his password.

With requestMatchers("/authenticate").permitAll() our authentication endpoint is freely accessible, but because of anyRequest().hasRole(USER) the role USER is required for all other request. Spring Security automatically adds the ROLE_ prefix, so only the short form is passed here.

SessionCreationPolicy.STATELESS is used to specify that Spring Security does not create or access a session. Also JwtRequestFilter is added at a proper position in our filter chain, so the SecurityContext can be updated before the role is actually checked.

Conclusion

With this minimal setup, our application is secured using Spring Security and JWT. It can be extended according to our own requirements, for example to define the required role directly at our endpoints with @PreAuthorize("hasRole('ROLE_USER')").

In the Professional plan of Bootify, a Spring Boot application with JWT setup can be generated using a table of the self-defined database schema. Get your runnable Spring Boot application with REST API and advanced features in minutes!

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