需求：用户数据可能来自不同的标，在认证的时候，如果第一张表没有查找到用户，就去第二张表中查询

数据源可能并不是都是数据库，可能有些用户信息来自内存，有些数据信息来自 Redis，有些用户信息来自数据库

@Configuration
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Autowired
    MyUserDetailsService myUserDetailsService;
    @Autowired
    MyUserDetailsService2 myUserDetailsService2;

    @Override
    @Bean
    public AuthenticationManager authenticationManagerBean() throws Exception {
        DaoAuthenticationProvider dao1 = new DaoAuthenticationProvider();
        dao1.setUserDetailsService(myUserDetailsService);

        DaoAuthenticationProvider dao2 = new DaoAuthenticationProvider();
        dao2.setUserDetailsService(myUserDetailsService2);

        ProviderManager manager = new ProviderManager(dao1, dao2);
        return manager;
    }

@Service
@Primary
public class MyUserDetailsService implements UserDetailsService {
    @Autowired
    UserMapper userMapper;
    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        User user = userMapper.loadUserByUsername(username);
        if (user == null) {
            throw new UsernameNotFoundException("用户不存在");
        }
        user.setRoles(userMapper.getRolesByUid(user.getId()));
        return user;
    }
}