apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/configuration/AuthConfiguration.java/SpringSecurityLDAPConfigurer/userSearch
class SpringSecurityLDAPConfigurer:    @Bean
    public FilterBasedLdapUserSearch userSearch() {
      if (ldapExtendProperties.getGroup() == null || StringUtils
          .isBlank(ldapExtendProperties.getGroup().getGroupSearch())) {
        FilterBasedLdapUserSearch filterBasedLdapUserSearch = new FilterBasedLdapUserSearch("",
            ldapProperties.getSearchFilter(), ldapContextSource
        );
        filterBasedLdapUserSearch.setSearchSubtree(true);
        return filterBasedLdapUserSearch;
      }

      FilterLdapByGroupUserSearch filterLdapByGroupUserSearch = new FilterLdapByGroupUserSearch(
          ldapProperties.getBase(), ldapProperties.getSearchFilter(), ldapExtendProperties.getGroup().getGroupBase(),
          ldapContextSource, ldapExtendProperties.getGroup().getGroupSearch(),
          ldapExtendProperties.getMapping().getRdnKey(),
          ldapExtendProperties.getGroup().getGroupMembership(), ldapExtendProperties.getMapping().getLoginId()
      );
      filterLdapByGroupUserSearch.setSearchSubtree(true);
      return filterLdapByGroupUserSearch;
    }