apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/configuration/AuthConfiguration.java/SpringSecurityLDAPAuthAutoConfiguration/springSecurityUserService
class SpringSecurityLDAPAuthAutoConfiguration:    @Bean
    @ConditionalOnMissingBean(UserService.class)
    public UserService springSecurityUserService() {
      return new LdapUserService();
    }