Spring Security Authentication Provider

1. Overview

In this tutorial, we'll learn how to set up an Authentication Provider in Spring Security, allowing for additional flexibility compared to the standard scenario using a simple UserDetailsService.

2. The Authentication Provider

Spring Security provides a variety of options for performing authentication. These options follow a simple contract; an Authentication request is processed by an AuthenticationProvider, and a fully authenticated object with full credentials is returned.

The standard and most common implementation is the DaoAuthenticationProvider, which retrieves the user details from a simple, read-only user DAO, the UserDetailsService. This User Details Service only has access to the username in order to retrieve the full user entity, which is enough for most scenarios.

More custom scenarios will still need to access the full Authentication request to be able to perform the authentication process. For example, when authenticating against some external, third party service (such as Crowd), both the username and password from the authentication request will be necessary.

For these more advanced scenarios, we'll need to define a custom Authentication Provider:

@Component
public class CustomAuthenticationProvider implements AuthenticationProvider {

    @Override
    public Authentication authenticate(Authentication authentication) 
      throws AuthenticationException {
 
        String name = authentication.getName();
        String password = authentication.getCredentials().toString();
        
        if (shouldAuthenticateAgainstThirdPartySystem()) {
 
            // use the credentials
            // and authenticate against the third-party system
            return new UsernamePasswordAuthenticationToken(
              name, password, new ArrayList<>());
        } else {
            return null;
        }
    }

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

Notice that the granted authorities set on the returned Authentication object are empty. This is because authorities are, of course, application specific.

3. Register the Auth Provider

Now that we've defined the Authentication Provider, we need to specify it in the XML Security Configuration using the available namespace support:

<http use-expressions="true">
    <intercept-url pattern="/**" access="isAuthenticated()"/>
    <http-basic/>
</http>

<authentication-manager>
    <authentication-provider
      ref="customAuthenticationProvider" />
</authentication-manager>

4. Java Configuration

Next, we'll take a look at the corresponding Java configuration:

@Configuration
@EnableWebSecurity
@ComponentScan("com.baeldung.security")
public class SecurityConfig {

    @Autowired
    private CustomAuthenticationProvider authProvider;

    @Bean
    public AuthenticationManager authManager(HttpSecurity http) throws Exception {
        AuthenticationManagerBuilder authenticationManagerBuilder = 
            http.getSharedObject(AuthenticationManagerBuilder.class);
        authenticationManagerBuilder.authenticationProvider(authProvider);
        return authenticationManagerBuilder.build();
    }

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http.authorizeRequests()
            .anyRequest()
            .authenticated()
            .and()
            .httpBasic();
        return http.build();
    }

}

5. Performing Authentication

Requesting Authentication from the Client is basically the same with or without this custom authentication provider on the back end.

We'll use a simple curl command to send an authenticated request:

curl --header "Accept:application/json" -i --user user1:user1Pass 
    http://localhost:8080/spring-security-custom/api/foo/1

For the purposes of this example, we secured the REST API with Basic Authentication.

And we get back the expected 200 OK from the server:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Set-Cookie: JSESSIONID=B8F0EFA81B78DE968088EBB9AFD85A60; Path=/spring-security-custom/; HttpOnly
Content-Type: application/json;charset=UTF-8
Transfer-Encoding: chunked
Date: Sun, 02 Jun 2013 17:50:40 GMT

6. Conclusion

In this article, we explored an example of a custom authentication provider for Spring Security.

The full implementation of this article can be found in the GitHub project.

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