code: func (api *API) FirewallRule(zoneID, firewallRuleID string) (FirewallRule, error) {
  	uri := fmt.Sprintf("/zones/%s/firewall/rules/%s", zoneID, firewallRuleID)
  
  	res, err := api.makeRequest("GET", uri, nil)
  	if err != nil {
  		return FirewallRule{}, errors.Wrap(err, errMakeRequestError)
  	}
  
  	var firewallRuleResponse FirewallRuleResponse
  	err = json.Unmarshal(res, &firewallRuleResponse)
  	if err != nil {
  		return FirewallRule{}, errors.Wrap(err, errUnmarshalError)
  	}
  
  	return firewallRuleResponse.Result, nil
  }
docs: // FirewallRule returns a single firewall rule based on the ID.
  //
  // API reference: https://developers.cloudflare.com/firewall/api/cf-firewall-rules/get/#get-by-rule-id