code: func (a *authenticator) validateCredentials(credentials *credentials) (string, int, error) {
  	user, err := a.userDb.GetUser(credentials.Username)
  	if err != nil {
  		return "", http.StatusUnauthorized, errors.Errorf("401 unauthorized: user name or password is incorrect")
  	}
  	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(credentials.Password)); err != nil {
  		return credentials.Username, http.StatusUnauthorized, fmt.Errorf("401 unauthorized: user name or password is incorrect")
  	}
  	return credentials.Username, 0, nil
  }
docs: // Validates credentials, returns name and error code/message if invalid