How to alter instance which built from Spring Security Configurer

# Interface *org.springframework.security.config.annotation.ObjectPostProcessor*

On Spring Security configurer/builder, they are designed for to accept one or more instance contains *ObjectPostProcessor* interface. Below is the definition.

```java
public interface ObjectPostProcessor<T> {
  <O extends T> O postProcess(O object);
}
```

**postProcess()** method is for alter instance which pass into it.

There is a *ObjectPostProcessor* implementation class: *org.springframework.security.config.annotation.configuration.AutowireBeanFactoryObjectPostProcessor*. The job of this class

1. initialized instance (including inject prerequisite instance by using *ApplicationContext*) which passed into it
2. it call *SmartInitializingSingleton*, *DisposableBean* interface methods of instance which processed before when same methods being called from *ApplicationContext* against it

A singleton instance of *AutowireBeanFactoryObjectPostProcessor* bean is created and be inject into configurer/builder when created. (This is the first *ObjectPostProcessor* if that configurer/builder accepts more than one *ObjectPostProcessor*)

Some configurer/builder can accept more than one *ObjectPostProcessor*. So alter instance which built from these configurer/builder is possible.

# Example

First get a copy of my [notice board example application](https://github.com/saladlam/spring-noticeboard). Add below file into *info.saladlam.example.spring.noticeboard.support* package.

```java
package info.saladlam.example.spring.noticeboard.support;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.security.config.annotation.ObjectPostProcessor;

public class CustomizeObjectPostProcessor implements ObjectPostProcessor<Object> {

	private static final Logger log = LoggerFactory.getLogger(CustomizeObjectPostProcessor.class);
	private String fromClass;

	public CustomizeObjectPostProcessor(String fromClass) {
		this.fromClass = fromClass;
	}

	public <T> T postProcess(T object) {
		log.info("Instance pass into {}: {}", this.fromClass, object.getClass().getName());
		return object;
	}

}
```

Then alter **configure()** method in class *info.saladlam.example.spring.noticeboard.config.WebSecurityConfig* to following.

```java
	@Override
	protected void configure(HttpSecurity http) throws Exception {
		http.authorizeRequests()
				// must put more restricted rule at first
				.antMatchers("/manage/*/approve").hasAuthority("ADMIN")
				.antMatchers("/manage/**").hasAuthority("USER")
			.and()
				.httpBasic().disable()
				.formLogin()
					.loginPage("/login")
					.loginProcessingUrl("/loginHandler")
					.failureUrl("/login?error=true")
					.permitAll()
			.and()
				.logout().logoutSuccessUrl("/");

		http.authorizeRequests().withObjectPostProcessor(new CustomizeObjectPostProcessor("authorizeRequests"));
		http.formLogin().addObjectPostProcessor(new CustomizeObjectPostProcessor("formLogin"));
		http.httpBasic().addObjectPostProcessor(new CustomizeObjectPostProcessor("httpBasic"));
		http.logout().addObjectPostProcessor(new CustomizeObjectPostProcessor("logout"));
	}
```

Finally you may see following in log message.

```
2019-09-16 12:25:54.503  INFO 5512 --- [  restartedMain] i.s.e.s.n.s.CustomizeObjectPostProcessor : Instance pass into formLogin: org.springframework.security.web.authentication.LoginUrlAuthenticationEntryPoint
2019-09-16 12:25:56.121  INFO 5512 --- [  restartedMain] i.s.e.s.n.s.CustomizeObjectPostProcessor : Instance pass into httpBasic: org.springframework.security.web.authentication.DelegatingAuthenticationEntryPoint
2019-09-16 12:25:57.009  INFO 5512 --- [  restartedMain] i.s.e.s.n.s.CustomizeObjectPostProcessor : Instance pass into httpBasic: org.springframework.security.web.authentication.logout.HttpStatusReturningLogoutSuccessHandler
2019-09-16 12:25:58.145  INFO 5512 --- [  restartedMain] i.s.e.s.n.s.CustomizeObjectPostProcessor : Instance pass into logout: org.springframework.security.web.authentication.logout.LogoutFilter
2019-09-16 12:25:59.732  INFO 5512 --- [  restartedMain] i.s.e.s.n.s.CustomizeObjectPostProcessor : Instance pass into authorizeRequests: org.springframework.security.web.access.expression.DefaultWebSecurityExpressionHandler
2019-09-16 12:26:00.798  INFO 5512 --- [  restartedMain] i.s.e.s.n.s.CustomizeObjectPostProcessor : Instance pass into authorizeRequests: org.springframework.security.access.vote.AffirmativeBased
2019-09-16 12:29:01.005  INFO 5512 --- [  restartedMain] i.s.e.s.n.s.CustomizeObjectPostProcessor : Instance pass into authorizeRequests: org.springframework.security.web.access.intercept.FilterSecurityInterceptor
2019-09-16 12:29:03.527  INFO 5512 --- [  restartedMain] i.s.e.s.n.s.CustomizeObjectPostProcessor : Instance pass into formLogin: org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter
2019-09-16 12:29:03.933  INFO 5512 --- [  restartedMain] i.s.e.s.n.s.CustomizeObjectPostProcessor : Instance pass into httpBasic: org.springframework.security.web.authentication.www.BasicAuthenticationFilter
```

By designs *CustomizeObjectPostProcessor* class, you may alter instance pass into it.

# Appendix: list of class instance created by Spring Security configurer/builder

| Spring Security configurer/builder                                                                                      | Class instance built                                                                                                                                                                                                                                          |
| ----------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| org.springframework.security.config.annotation.authentication.configurers.provisioning.JdbcUserDetailsManagerConfigurer | org.springframework.security.authentication.dao.DaoAuthenticationProvider                                                                                                                                                                                     |
| org.springframework.security.config.annotation.web.configurers.CsrfConfigurer                                           | org.springframework.security.web.csrf.CsrfFilter                                                                                                                                                                                                              |
| org.springframework.security.config.annotation.web.configurers.ExceptionHandlingConfigurer                              | org.springframework.security.web.access.ExceptionTranslationFilter                                                                                                                                                                                            |
| org.springframework.security.config.annotation.web.configurers.HeadersConfigurer                                        | org.springframework.security.web.header.HeaderWriterFilter                                                                                                                                                                                                    |
| org.springframework.security.config.annotation.web.configurers.SessionManagementConfigurer                              | org.springframework.security.web.authentication.session.ChangeSessionIdAuthenticationStrategy, org.springframework.security.web.authentication.session.CompositeSessionAuthenticationStrategy, org.springframework.security.web.session.SessionManagementFilter |
| org.springframework.security.config.annotation.web.configurers.SecurityContextConfigurer                                | org.springframework.security.web.context.SecurityContextPersistenceFilter                                                                                                                                                                                     |
| org.springframework.security.config.annotation.web.configurers.RequestCacheConfigurer                                   | org.springframework.security.web.savedrequest.RequestCacheAwareFilter                                                                                                                                                                                         |
| org.springframework.security.config.annotation.web.configurers.AnonymousConfigurer                                      | org.springframework.security.authentication.AnonymousAuthenticationProvider                                                                                                                                                                                   |
| org.springframework.security.config.annotation.web.configurers.ServletApiConfigurer                                     | org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter                                                                                                                                                                           |
| org.springframework.security.config.annotation.web.configurers.LogoutConfigurer                                         | org.springframework.security.web.authentication.logout.LogoutFilter                                                                                                                                                                                           |
| org.springframework.security.config.annotation.web.configurers.ExpressionUrlAuthorizationConfigurer                     | org.springframework.security.web.access.expression.DefaultWebSecurityExpressionHandler, org.springframework.security.access.vote.AffirmativeBasedorg.springframework.security.web.access.intercept.FilterSecurityInterceptor                                   |
| org.springframework.security.config.annotation.web.configurers.FormLoginConfigurer                                      | org.springframework.security.web.authentication.LoginUrlAuthenticationEntryPoint, org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter                                                                                         |