Added middleware

Author: alexivsn

README.md

@@ -40,5 +40,11 @@ $sn->track(array(
         'id' => '12345'
     ]
 ));
-    
+
+
+middleware:
+
+$body = file_get_contents('php://input');
+$sn->middleware->verifySignature($_SERVER, $body)
+
 ```

src/middleware.php

@@ -0,0 +1,20 @@
+<?php
+
+const SIGNATURE_KEY = 'x-securenative';
+
+class Middleware
+{
+  private $apiKey;
+
+  public function __construct($apiKey)
+  {
+      $this->apiKey = $apiKey;
+  }
+
+  public function verifySignature($headers, $body)
+  {
+     $signature = headers[SIGNATURE_KEY] ? headers[SIGNATURE_KEY] : "";
+     $comparison_signature = hash_hmac('sha512', Utils::serialize($body), $this->apiKey, true);
+     return hash_equals($signature, $comparison_signature);
+  }
+}

src/securenative.php

@@ -3,6 +3,7 @@
 //
 
 require "event-manager.php";
+require "middleware.php";
 require "Models/event-options.php";
 require "Models/verify-result.php";
 require "Enums/risk-levels.php";
@@ -14,6 +15,7 @@ class SecureNative
   private static $apiKey;
   private static $options;
   private static $eventManager;
+  private static $middleware;
 
   public static function init($apiKey, SecureNativeOptions $secureNativeOptions)
   {
@@ -24,6 +26,7 @@ public static function init($apiKey, SecureNativeOptions $secureNativeOptions)
       self::$apiKey = $apiKey;
       self::$options = $secureNativeOptions;
       self::$eventManager = new EventManager($apiKey, self::$options);
+      self::$middleware = new Middleware($apiKey);
   }
 
   public static function track(Array $attributes)