Handle both old HPP and the new checkout api flow

Response will be handled in PW-705

Controller/Process/Result.php

@@ -302,6 +302,7 @@ class Result extends \Magento\Framework\App\Action\Action
     protected function _authenticate($response)
     {
 
+    	if (!empty($response['merchantSig'])) {
 			$merchantSigNotification = $response['merchantSig'];
 
         // do it like this because $_GET is converting dot to underscore
@@ -326,8 +327,11 @@ class Result extends \Magento\Framework\App\Action\Action
 			if (strcmp($merchantSig, $merchantSigNotification) === 0) {
 				return true;
 			}
-
 			return false;
+		} else{
+    		// send the payload verification payment\details request to validate the response
+
+		}
 
     }