Spring Security疑问：内存认证中withUser方法的来源

Great question—this is a super common point of confusion with Spring Security 4.x, and I’ve been there myself! Let’s break this down clearly:

The Method Doesn’t Belong to AuthenticationManagerBuilder #

You’re not missing anything in the AuthenticationManagerBuilder docs—because withUser() isn’t actually a method on that class. Here’s what’s happening in your code chain:
When you call auth.inMemoryAuthentication(), you’re no longer working with an AuthenticationManagerBuilder instance. That method returns an InMemoryUserDetailsManagerConfigurer<AuthenticationManagerBuilder> object, and withUser() is defined on this configurer class (it inherits the method from its parent class UserDetailsManagerConfigurer).

To visualize the chain:

// auth = AuthenticationManagerBuilder instance
InMemoryUserDetailsManagerConfigurer<AuthenticationManagerBuilder> configurer = auth.inMemoryAuthentication();
UserBuilder userBuilder = configurer.withUser("poef"); // This is where withUser() comes from
userBuilder.password("fump").roles("ACTUATOR");

So if you only checked the AuthenticationManagerBuilder docs, you’d never spot withUser()—you need to look up the docs for InMemoryUserDetailsManagerConfigurer instead.

A Critical Note for Your 4.2.5 Setup #

One quick heads-up: Spring Security 4.x blocks plain-text passwords by default. Your current code with "fump" as a raw password will throw an error unless you add a password encoder. Here’s how to fix that properly:

import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;

// ...

@Override
protected void configure(AuthenticationManagerBuilder auth) throws Exception {
    BCryptPasswordEncoder passwordEncoder = new BCryptPasswordEncoder();
    auth.inMemoryAuthentication()
        .passwordEncoder(passwordEncoder)
        .withUser("poef")
        .password(passwordEncoder.encode("fump"))
        .roles("ACTUATOR");
}

This ensures your password is hashed and compliant with Spring Security’s security defaults.

内容的提问来源于stack exchange，提问作者user9183621