code: func (c *AuthorizationService) Get(authzURL string) (acme.Authorization, error) {
  	if len(authzURL) == 0 {
  		return acme.Authorization{}, errors.New("authorization[get]: empty URL")
  	}
  
  	var authz acme.Authorization
  	_, err := c.core.postAsGet(authzURL, &authz)
  	if err != nil {
  		return acme.Authorization{}, err
  	}
  	return authz, nil
  }
docs: // Get Gets an authorization.