Why does overwriting a method( configure(AuthenticationManagerBuilder builder) ) influence a local AuthenticationManager?Not global?

[jqws-1997]

The author hello！
I looked at the documentation on the website, and it says this:

@Configuration
public class ApplicationSecurity extends WebSecurityConfigurerAdapter {

  @Autowired
  DataSource dataSource;

   ... // web stuff here

  @Override
  public void configure(AuthenticationManagerBuilder builder) {
    builder.jdbcAuthentication().dataSource(dataSource).withUser("dave")
      .password("secret").roles("USER");
  }

}
If we had used an @Override of a method in the configurer, the AuthenticationManagerBuilder would be used only to build a “local” AuthenticationManager, which would be a child of the global one. In a Spring Boot application, you can @Autowired the global one into another bean, but you cannot do that with the local one unless you explicitly expose it yourself.
If we rewrote the method (configure) ,WebSecurityConfigurerAdapter`s  disableLocalConfigureAuthenticationBldr  is not true.

But I was a little confused in the process of using it, and I think the end result is a global one.

configure(AuthenticationManagerBuilder auth) Not rewritten：

protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        //If we rewrote the method ,it is not true.
        this.disableLocalConfigureAuthenticationBldr = true;
    }

getHttp():

if (this.http != null) {
            return this.http;
        } else {
            DefaultAuthenticationEventPublisher eventPublisher = (DefaultAuthenticationEventPublisher)this.objectPostProcessor.postProcess(new DefaultAuthenticationEventPublisher());
            this.localConfigureAuthenticationBldr.authenticationEventPublisher(eventPublisher);
            //fellow authenticationManager()
            AuthenticationManager authenticationManager = this.authenticationManager();
            // It is parentAuthenticationManager ()
            this.authenticationBuilder.parentAuthenticationManager(authenticationManager);
            .......

authenticationManager():

protected AuthenticationManager authenticationManager() throws Exception {
        if (!this.authenticationManagerInitialized) {
            // This is the method that we overwrote（configure）
            this.configure(this.localConfigureAuthenticationBldr);
            if (this.disableLocalConfigureAuthenticationBldr) {
                this.authenticationManager = this.authenticationConfiguration.getAuthenticationManager();
            } else {
                //disableLocalConfigureAuthenticationBldr is not true
                //Overridden methods（configure） are used for the localConfigureAuthenticationBldr 
                this.authenticationManager = (AuthenticationManager)this.localConfigureAuthenticationBldr.build();
            }

            this.authenticationManagerInitialized = true;
        }

        return this.authenticationManager;
    }

So I think you end up with a global authenticationManager instead of a local authenticationManager.
Maybe my English is too poor to understand what the author says. I hope you can give me some advice. Thank you~