Spring Security – JWT Authentication Architecture | Spring Boot

In this tutorial, we’re gonna look at Spring Security Architecture built for JWT Authentication that helps us secure our REST APIs with JWT (JSON Web Token) authentication.

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Spring Security JWT Authentication architecture

This is diagram for Spring Security/JWT classes that are separated into 3 layers:
– HTTP
– Spring Security
– REST API

Look at the diagram above, we can easily associate these components with Spring Security Authentication process: receive HTTP request, filter, authenticate, store Authentication data, generate token, get User details, authorize, handle exception…

At a glance:
– SecurityContextHolder provides access to the SecurityContext.
– SecurityContext holds the Authentication and possibly request-specific security information.
– Authentication represents the principal which includes GrantedAuthority that reflects the application-wide permissions granted to a principal.
– UserDetails contains necessary information to build an Authentication object from DAOs or other source of security data.
– UserDetailsService helps to create a UserDetails from a String-based username and is usually used by AuthenticationProvider.
– JwtAuthTokenFilter (extends OncePerRequestFilter) pre-processes HTTP request, from Token, create Authentication and populate it to SecurityContext.
– JwtProvider validates, parses token String or generates token String from UserDetails.
– UsernamePasswordAuthenticationToken gets username/password from login Request and combines into an instance of Authentication interface.
– AuthenticationManager uses DaoAuthenticationProvider (with help of UserDetailsService & PasswordEncoder) to validate instance of UsernamePasswordAuthenticationToken, then returns a fully populated Authentication instance on successful authentication.
– SecurityContext is established by calling SecurityContextHolder.getContext().setAuthentication(…​) with returned authentication object above.
– AuthenticationEntryPoint handles AuthenticationException.
– Access to Restful API is protected by HTTPSecurity and authorized with Method Security Expressions.

Receive HTTP Request

When a HTTP request comes (from a browser, a web service client, an HttpInvoker or an AJAX application – Spring doesn’t care), it will go through a chain of filters for authentication and authorization purposes.

So, it is also true for a User Authentication request, that filter chain will be applied until relevant Authentication Filter is found.

Filter the Request

In this architecture, we add our JwtAuthTokenFilter (that extends Spring OncePerRequestFilter abstract class) to the chain of filters.

class WebSecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        ...
        http.addFilterBefore(authenticationJwtTokenFilter(), UsernamePasswordAuthenticationFilter.class);
    }
}

JwtAuthTokenFilter validates the Token using JwtProvider:

class JwtAuthTokenFilter extends OncePerRequestFilter {
    @Autowired
    private JwtProvider tokenProvider;

    @Override
    protected void doFilterInternal(...) {
        String jwt = getJwt(request);
        if (jwt!=null && tokenProvider.validateJwtToken(jwt)) {
            ...
        }
        filterChain.doFilter(request, response);
    }
}

Now we have 2 cases:
– Login/SignUp: RestAPI with non-protected APIs -> authenticate Login Request with AuthenticationManager, if error occurs, handle AuthenticationException with AuthenticationEntryPoint.
– With protected Resources:
+ jwt token is null/invalid -> if Authenticated Error occurs, handle AuthenticationException with AuthenticationEntryPoint.
+ jwt token is valid -> from token, get User information, then create AuthenticationToken.

Create AuthenticationToken from Token

JwtAuthTokenFilter extracts username/password from the received token using JwtProvider, then based on the extracted data, JwtAuthTokenFilter:
– creates a AuthenticationToken (that implements Authentication)
– uses the AuthenticationToken as Authentication object and stores it in the SecurityContext for future filter uses (e.g: Authorization filters).

In this tutorial, we use UsernamePasswordAuthenticationToken:

// extract user information
String username = tokenProvider.getUserNameFromJwtToken(jwt);
UserDetails userDetails = userDetailsService.loadUserByUsername(username);

// create AuthenticationToken
UsernamePasswordAuthenticationToken authentication
        = new UsernamePasswordAuthenticationToken(userDetails, null, userDetails.getAuthorities());
authentication.setDetails(new WebAuthenticationDetailsSource().buildDetails(request));

Store Authentication object in SecurityContext

SecurityContextHolder.getContext().setAuthentication(authentication);

SecurityContextHolder is the most fundamental object where we store details of the present security context of the application (includes details of the principal). Spring Security uses an Authentication object to represent this information and we can query this Authentication object from anywhere in our application:

Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
// currently authenticated user
Object principal = authentication.getPrincipal();

getContext() returns an instance of SecurityContext interface that holds the Authentication and possibly request-specific security information.

Delegate AuthenticationToken for AuthenticationManagager

After AuthenticationToken object was created, it will be used as input parameter for authenticate() method of the AuthenticationManager:

public interface AuthenticationManager {
    Authentication authenticate(Authentication authentication)
            throws AuthenticationException;
}

We can see that AuthenticationManager is just an interface, the default implementation in Spring Security is ProviderManager:

public class ProviderManager implements AuthenticationManager, ... {
    private List providers;
}

Authenticate with AuthenticationProvider

AuthenticationProviders

ProviderManager delegates to a list of configured AuthenticationProviders, each of them will try to authenticate the User, then either throw an exception or return a fully populated Authentication object:

public class ProviderManager implements AuthenticationManager, ... {
    private List providers;

    public Authentication authenticate(Authentication authentication) throws AuthenticationException {
        for (AuthenticationProvider provider : getProviders()) {
            ...
            try {
                ...
                result = provider.authenticate(authentication);
                if (result != null) {
                    copyDetails(authentication, result);
                    break;
                }
            }
            catch (Exception...) {}
            ...
            return result;
        }
    }
}

These are some authentication providers that Spring Framework provides:

• DaoAuthenticationProvider
• PreAuthenticatedAuthenticationProvider
• LdapAuthenticationProvider
• ActiveDirectoryLdapAuthenticationProvider
• JaasAuthenticationProvider
• CasAuthenticationProvider
• RememberMeAuthenticationProvider
• AnonymousAuthenticationProvider
• RunAsImplAuthenticationProvider
• OpenIDAuthenticationProvider

DaoAuthenticationProvider

DaoAuthenticationProvider works well with form-based logins or HTTP Basic authentication which submits a simple username/password authentication request.
It authenticates the User simply by comparing the password submitted in a UsernamePasswordAuthenticationToken against the one loaded by the UserDetailsService (as a DAO):

@Autowired
AuthenticationManager authenticationManager;
...
Authentication authentication = 
				authenticationManager.authenticate(
				    new UsernamePasswordAuthenticationToken(loginRequest.username, loginRequest.password)
				);

Configuring this provider is simple with AuthenticationManagerBuilder:

class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Autowired
    UserDetailsServiceImpl userDetailsService;

    @Override
    public void configure(AuthenticationManagerBuilder authenticationManagerBuilder) throws Exception {
        authenticationManagerBuilder
                .userDetailsService(userDetailsService)
                .passwordEncoder(passwordEncoder());
    }

    @Bean
    @Override
    public AuthenticationManager authenticationManagerBean() throws Exception {
        return super.authenticationManagerBean();
    }
}

Retrieve User details with UserDetailsService

We can obtain a principal from the Authentication object. This principal can be cast into a UserDetails object to lookup the username, password and GrantedAuthoritys.

Therefore, after authenticating is successful, we can simply get UserDetails from Authentication object:

UserDetails userDetails = (UserDetails) authentication.getPrincipal();
// userDetails.getUsername()
// userDetails.getPassword()
// userDetails.getAuthorities()

DaoAuthenticationProvider also uses UserDetailsService for getting UserDetails object. This is the common approach in which we only pass a String-based ‘username’ argument and returns a UserDetails:

public interface UserDetailsService {
    UserDetails loadUserByUsername(String username) throws UsernameNotFoundException;
}

It is simple to implement UserDetailsService and easy for us to retrieve authentication information using a persistence strategy:

@Service
public class UserDetailsServiceImpl implements UserDetailsService {
    @Autowired
    UserRepository userRepository;

    @Override
    @Transactional
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {

    	User user = userRepository.findByUsername(username).orElseThrow(
    			() -> new UsernameNotFoundException("User Not Found with -> username or email : " + username));

    	return UserPrinciple.build(user); // UserPrinciple implements UserDetails
    }
}

Get GrantedAuthority

Another important method provided by Authentication is getAuthorities() that provides an collection of GrantedAuthority objects:

public interface Authentication extends Principal, Serializable {
    Collection getAuthorities();
}

A GrantedAuthority is an authority that is granted to the principal. Such authorities are usually ‘roles’, such as ROLE_ADMIN, ROLE_PM, ROLE_USER…

Protect Resources with HTTPSecurity & Method Security Expressions

Configure HTTPSecurity

To help Spring Security know when we want to require all users to be authenticated, which Exception Handler to be chosen, which filter and when we want it to work. We implement WebSecurityConfigurerAdapter and provide a configuration in the configure(HttpSecurity http) method:

@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.cors().and().csrf().disable().
                authorizeRequests()
                .antMatchers("/api/auth/**").permitAll()
                .anyRequest().authenticated()
                .and()
                .exceptionHandling().authenticationEntryPoint(unauthorizedHandler).and()
                ...;
        
        http.addFilterBefore(authenticationJwtTokenFilter(), UsernamePasswordAuthenticationFilter.class);
    }
}

Method Security Expressions

Spring Security provides some annotations for pre and post-invocation authorization checks, filtering of submitted collection arguments or return values: @PreAuthorize, @PreFilter, @PostAuthorize and @PostFilter.

To enable Method Security Expressions, we use @EnableGlobalMethodSecurity annotation:

@EnableGlobalMethodSecurity(prePostEnabled = true)
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    ...
}

In the code below, we use the most useful annotation @PreAuthorize to decide whether a method can actually be invoked or not:

@RestController
public class TestRestAPIs {
	
    @GetMapping("/api/test/user")
    @PreAuthorize("hasRole('USER') or hasRole('ADMIN')")
    public String userAccess() {
    	return ">>> User Contents!";
    }

    @GetMapping("/api/test/pm")
    @PreAuthorize("hasRole('PM') or hasRole('ADMIN')")
    public String projectManagementAccess() {
    	return ">>> Project Management Board";
    }
	
    @GetMapping("/api/test/admin")
    @PreAuthorize("hasRole('ADMIN')")
    public String adminAccess() {
        return ">>> Admin Contents";
    }
}

Handle AuthenticationException – AuthenticationEntryPoint

If the user requests a secure HTTP resource without being authenticated, AuthenticationEntryPoint will be called. At this time, an AuthenticationException is thrown, commence() method on the entry point is triggered:

@Component
public class JwtAuthEntryPoint implements AuthenticationEntryPoint {
   
    @Override
    public void commence(HttpServletRequest request,
                         HttpServletResponse response,
                         AuthenticationException e) 
                            throws IOException, ServletException {
    	
        logger.error("Unauthorized error. Message - {}", e.getMessage());
        response.sendError(HttpServletResponse.SC_UNAUTHORIZED, "Error -> Unauthorized");
    }
}