code: func (s *IdentityService) UpsertTOTP(user string, secretKey string) error {
  	if user == "" {
  		return trace.BadParameter("missing user name")
  	}
  
  	item := backend.Item{
  		Key:   backend.Key(webPrefix, usersPrefix, user, totpPrefix),
  		Value: []byte(secretKey),
  	}
  
  	_, err := s.Put(context.TODO(), item)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  
  	return nil
  }
docs: // UpsertTOTP upserts TOTP secret key for a user that can be used to generate and validate tokens.