code: func (state *UserState) ConfirmUserByConfirmationCode(confirmationcode string) error {
  	username, err := state.FindUserByConfirmationCode(confirmationcode)
  	if err != nil {
  		return err
  	}
  	state.Confirm(username)
  	return nil
  }
docs: // Take a confirmation code and mark the corresponding unconfirmed user as confirmed.