code: func MapUsernamesToIdentifiers(usernames []string, valMgr *validation.Manager) (map[string]string, error) {
  	identifiers := map[string]string{}
  	emails, err := valMgr.GetValidatedEmailAddressesByUsernames(usernames)
  	if err != nil {
  		return identifiers, err
  	}
  	for _, validatedEmail := range emails {
  		identifiers[validatedEmail.EmailAddress] = validatedEmail.Username
  	}
  	validatedPhoneNumbers, err := valMgr.GetValidatedPhoneNumbersByUsernames(usernames)
  	if err != nil {
  		return identifiers, err
  	}
  	for _, validatedPhone := range validatedPhoneNumbers {
  		identifiers[validatedPhone.Phonenumber] = validatedPhone.Username
  	}
  	return identifiers, nil
  }
docs: // MapUsernamesToIdentifiers returns a map with as key the validated information (identifier) and as value the username