How to Properly Inject AuthenticationManager in a Custom Filter Using Java Configuration

How do I inject the AuthenticationManager into my custom filter using Java configuration in Spring Security?

@Autowired
private AuthenticationManager authenticationManager;

Injecting the `AuthenticationManager` into a custom filter can lead to issues such as `NoSuchBeanDefinitionException` if not configured correctly. This guide will walk you through the proper configuration steps in Spring Security using Java.

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

Causes

• The `AuthenticationManager` is not defined as a bean in your Java configuration.
• The custom filter may be instantiated without the necessary Spring context, resulting in failed dependency resolution.
• Incorrect configuration of the `WebSecurityConfigurerAdapter` methods that do not expose the `AuthenticationManager` bean.

Solutions

• Define an `AuthenticationManager` bean using `@Bean` in your `SecurityConfig` class.
• Override `authenticationManagerBean()` method in your `SecurityConfig` to expose the `AuthenticationManager` as a Spring bean.
• Ensure that the custom filter is instantiated and registered correctly within the Spring context.

Mistake: Forgetting to define the `AuthenticationManager` bean in the configuration.

Solution: Make sure to add the `@Bean` annotation for the `authenticationManagerBean()` method in your configuration class.

Mistake: Instantiating the custom filter manually instead of allowing Spring to manage it.

Solution: Always use `@Component` annotation for your filter to ensure it is managed by Spring.