Spring Boot Tutorial 0/110 lessons ~6 min read Lesson 39“Production-grade backends”

Authentication

Authentication answers who are you?.

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Focus

2 guided sections

Practice signal

Examples included

Career prep

Foundation builder

Introduction

Authentication answers who are you?. The user proves identity (password, token, certificate) and Spring Security loads a UserDetails + roles into the SecurityContext.

Informative example

Custom UserDetailsService backed by your DB:

@Service @RequiredArgsConstructor
public class DbUserDetailsService implements UserDetailsService {
  private final UserRepository users;

  @Override
  public UserDetails loadUserByUsername(String email) {
    return users.findByEmail(email)
        .map(u -> User.withUsername(u.getEmail())
            .password(u.getPasswordHash())
            .authorities(u.getRoles().stream()
                .map(r -> new SimpleGrantedAuthority("ROLE_" + r))
                .toList())
            .build())
        .orElseThrow(() -> new UsernameNotFoundException(email));
  }
}

@Bean PasswordEncoder passwordEncoder() { return new BCryptPasswordEncoder(); }

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