如何使用Java中的认证和授权框架实现用户的身份验证和权限管理？

<authentication-manager>
    <authentication-provider user-service-ref="userDetailsService"/>
</authentication-manager>

@Service
public class CustomUserDetailsService implements UserDetailsService {
    @Autowired
    private UserRepository userRepository;
    
    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        User user = userRepository.findByUsername(username);
        if (user == null) {
            throw new UsernameNotFoundException("User not found with username: " + username);
        }
        return new org.springframework.security.core.userdetails.User(user.getUsername(), user.getPassword(), getAuthorities(user.getRoles()));
    }
    
    private Collection<? extends GrantedAuthority> getAuthorities(Collection<Role> roles) {
        return roles.stream().map(role -> new SimpleGrantedAuthority(role.getName())).collect(Collectors.toList());
    }
}

CREATE TABLE users (
    id BIGINT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    password VARCHAR(100) NOT NULL
);

CREATE TABLE roles (
    id BIGINT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(50) NOT NULL
);

CREATE TABLE user_roles (
    user_id BIGINT,
    role_id BIGINT,
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (role_id) REFERENCES roles(id),
    PRIMARY KEY (user_id, role_id)
);

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Autowired
    private UserDetailsService userDetailsService;
    
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/").permitAll()
                .antMatchers("/admin/**").hasRole("ADMIN")
                .anyRequest().authenticated()
                .and()
            .formLogin()
                .loginPage("/login")
                .permitAll()
                .and()
            .logout()
                .permitAll();
    }
    
    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
        auth.userDetailsService(userDetailsService).passwordEncoder(passwordEncoder());
    }
    
    @Bean
    public PasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder();
    }
}

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/admin/**").access("hasRole('ADMIN')")
                .anyRequest().authenticated();
    }
}

@RestController
@RequestMapping("/api")
public class ApiController {
    @PreAuthorize("hasRole('USER')")
    @GetMapping("/users")
    public List<User> getUsers() {
        // code here
    }
    
    @PreAuthorize("hasRole('ADMIN')")
    @PostMapping("/user")
    public User createUser(@RequestBody User user) {
        // code here
    }
}