Authorize.net signature timestamp

authorizenet_signature

<?php
namespace app\controllers\api;
use app\models\api\campaign\view\AuthorizePostbackRequest;
use yii\helpers\Url;
use app\components\ApiController;
use yii\helpers\Json;
use yii\web\ServerErrorHttpException;
use yii\db\Exception;
use yii\web\UnauthorizedHttpException;

class AuthorizenetController extends ApiController
{
	public function actionSignature()
	{
		$action="https://test.authorize.net/gateway/transact.dll";  //The url of where the Direct Post is going to take place
		$x_login=LOGIN_ID;                                    //the Login Id of authorize.net account
		$transaction_id=ACCOUNT_NUMBER;                         //The transaction id of Authorize.net account

		$x_relay_url= Url::to(['/postback/authorize-postback'], true);  //This return url of the Direct Post postback from Authorize.net-- in PostbackController

		$x_amount= $this->request->post('x_amount') ? $this->request->post('x_amount') : 0;

		if($x_amount && $x_amount > 0)
		{
			$x_fp_sequence	= rand(1, 1000);
			$x_fp_timestamp=time();
			$x_fp_hash= hash_hmac("md5", $x_login . "^" . $x_fp_sequence . "^" . $x_fp_timestamp . "^" . $x_amount . "^", $transaction_id);

			$response = [
				'action'=> $action,
				'x_login'=> $x_login,
				'x_fp_sequence'=> $x_fp_sequence,
				'x_fp_timestamp'=> $x_fp_timestamp,
				'x_fp_hash'=> $x_fp_hash,
				'x_relay_url'=> $x_relay_url
			];

			return $response;
		}
		else
		{
			throw new ServerErrorHttpException('Card amount must be greater than zero');
		}
 	}
}

This is an example of how to create an Authorize.net signature for the Direct Payment Method according to their guide here:
http://developer.authorize.net/api/upgrade_guide/