apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/spi/springsecurity/SpringSecurityUserInfoHolder.java/SpringSecurityUserInfoHolder/getCurrentUsername
class SpringSecurityUserInfoHolder:  private String getCurrentUsername() {
    Object principal = SecurityContextHolder.getContext().getAuthentication().getPrincipal();
    if (principal instanceof UserDetails) {
      return ((UserDetails) principal).getUsername();
    }
    if (principal instanceof Principal) {
      return ((Principal) principal).getName();
    }
    return String.valueOf(principal);
  }