Spring Security Authentication

Authentication

One of the fundamental ways to secure a resource is to make sure that the caller is who they claim to be. This process of checking credentials and making sure that they are genuine is called authentication.

This article will delve into the technical capabilities of Spring Security, specifically authentication. To find the complete code for this article, check out this GitHub repository.

The following diagram shows the fundamental process Spring Security uses to address this core security requirement. The figure is generic and can be used to explain all the various authentication methods that the framework supports:

Spring Security has a series of servlet filters (a filter chain). When a request reaches the server, it is intercepted by this series of filters (Step 1 in the preceding diagram). In the reactive world, with the new Spring WebFlux web application framework, filters are written quite differently from traditional filters, such as those used in the Spring MVC web application framework. Having said that, the fundamental mechanism remains the same for both.

The Servlet filter code execution in the filter chain keeps skipping until the right filter is reached. Once it reaches the right authentication filter based on the authentication mechanism used, it extracts the supplied credentials — most commonly a username and password — from the caller.

Using the supplied values (here, you have a username and password), the filter UsernamePasswordAuthenticationFilter creates an Authentication object. In the preceding diagram, the UsernamePasswordAuthenticationToken is created with the username and password supplied in Step 2. The Authentication object created in Step 2 is then used to call the authenticate method in the AuthenticationManager interface:

public interface AuthenticationManager {
    Authentication authenticate(Authentication authentication) throwsAuthenticationException;
}

The actual implementation is provided by the ProviderManager, which has a list of the configured AuthenticationProvider.

public interface AuthenticationProvider {
    Authentication authenticate(Authentication authentication) throwsAuthenticationException;
    boolean supports(Class<?> authentication);
}

The request passes through various providers and, in due course, tries to authenticate the request. There are a number of AuthenticationProvider interfaces as part of Spring Security.

In the diagram above, AuthenticationProvider requires user details (some providers require this, but some don’t), which are provided in UserDetailsService:

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

UserDetailsService retrieves UserDetails and implements the User interface using the supplied username.

If all goes well, Spring Security creates a fully populated Authentication object (authenticate: true, granted authority list, and username), which will contain various necessary details. The Authentication object is stored in the SecurityContext object by the filter for future use.

• An Authentication object with authenticated=true if Spring Security can validate the supplied user credentials
• An AuthenticationException if Spring Security finds that the supplied user credentials are invalid
•  null if Spring Security cannot decide whether it is true or false (confused state)

Setting Up the Authentication Manager

There are a number of built-inAuthenticationManagermethods in Spring Security that can be easily used in your application. Spring Security also has a number of helper classes, which you can set up using AuthenticationManager. One helper class is theAuthenticationManagerBuilder.

Using this class, it's quite easy to set up theUserDetailsService against a database, in memory, in LDAP, and so on. If the need arises, you could also have your own custom  UserDetailsService (maybe a custom single sign-on solution is already there in your organization).

You can make anAuthenticationManager global, so it will be accessible by your entire application. It will be available for method security and other WebSecurityConfigurerAdapter instances.

WebSecurityConfigurerAdapter is a class that is extended by your Spring configuration file, making it quite easy to bring Spring Security into your Spring application. This is how you set up a global  AuthenticationManager using the @Autowired annotation:

@Configuration
@EnableWebSecurity
public class SpringSecurityConfig extends WebSecurityConfigurerAdapter {
    @Autowired
    public void confGlobalAuthManager(AuthenticationManagerBuilderauth) throws Exception {
        auth
            .inMemoryAuthentication()
             .withUser("admin").password("admin@password").roles("ROLE_ADMIN");
    }
}

You can also create local the  AuthenticationManager, which is only available for this particular WebSecurityConfigurerAdapter by overriding the configure method, as shown in the following code:

@Configuration
@EnableWebSecurity
public class SpringSecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(AuthenticationManagerBuilderauth) throws Exception {
        auth
            .inMemoryAuthentication()
            .withUser("admin").password("admin@password").roles("ROLE_ADMIN");
}

Another option is to expose the  AuthenticationManager bean by overriding the  authenticationManagerBean method:

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

You can also expose various  AuthenticationManager, AuthenticationProvider, or the UserDetailsService as beans, which will override the default ones.

The preceding code example has used AuthenticationManagerBuilder to configure in-memory authentication.

AuthenticationProvider

AuthenticationProvider provides a mechanism for getting the user details with which authentication can be performed. Spring Security provides a number of AuthenticationProvider implementations, as shown in the following diagram:

Custom AuthenticationProvider

You can also write a custom supports like the  AuthenticationProvider by implementing the AuthenticationProvider interface. You have to implement two methods, namely, authenticate ( Authentication) and  Class<  ?  >aClass:

@Component
public class CustomAuthenticationProvider implements AuthenticationProvider {
    @Override
    public Authentication authenticate(Authentication authentication) throws AuthenticationException {
      String username = authentication.getName();
      String password = authentication.getCredentials().toString();

      if ("user".equals(username) && "password".equals(password)) {
            return new UsernamePasswordAuthenticationToken(username, password, Collections.emptyList());
       } else {
            throw new BadCredentialsException("Authentication failed");
       }
    }

    @Override
    public boolean supports(Class<?>aClass) {
        return aClass.equals(UsernamePasswordAuthenticationToken.class);
    }
}

On the GitHub page, navigate to the jetty-in-memory-basic-custom-authentication project to see the full source code of this class.

Multiple AuthenticationProvider

Spring Security allows you to declare multiple AuthenticationProvider implementations in your application. They are executed according to the order in which they are declared in the configuration.

The in jetty-in-memory-basic-custom-authentication project is modified further, and you have used the newly created CustomAuthenticationProvider as an AuthenticationProvider (Order 1) and the existing as your second  AuthenticationProvider (Order 2) —  MemoryAuthentication:

@EnableWebSecurity
@ComponentScan(basePackageClasses = CustomAuthenticationProvider.class)
public class SpringSecurityConfig extends WebSecurityConfigurerAdapter {
    @Autowired
    CustomAuthenticationProvidercustomAuthenticationProvider;

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.httpBasic()
            .and()
            .authorizeRequests()
            .antMatchers("/**")
            .authenticated(); // Use Basic authentication
    }

    @Override
    protected void configure(AuthenticationManagerBuilderauth) throws Exception {
        // Custom authentication provider - Order 1
        auth.authenticationProvider(customAuthenticationProvider);
        // Built-in authentication provider - Order 2
        auth.inMemoryAuthentication()
            .withUser("admin")
            .password("{noop}admin@password")
            //{noop} makes sure that the password encoder doesn't do anything
            .roles("ADMIN") // Role of the user
            .and()
            .withUser("user")
            .password("{noop}user@password")
            .credentialsExpired(true)
            .accountExpired(true)
            .accountLocked(true)
            .roles("USER");
    }
}

Whenever the authenticate method executes without error, the controls return, and, thereafter, the configured AuthenticationProvider doesn’t get executed.

If you found this article interesting, you can explore Hands-On Spring Security 5 for Reactive Applications to secure your Java applications by integrating the Spring Security framework in your code. Hands-On Spring Security 5 for Reactive Applications will guide you in integrating add-ons that will add value to any Spring Security module.

If you enjoyed this post, see more of Mohamed's articles here.