added ability to send appsecret_proof with request (#44)

* added ability to use appsecret_proof to request

* applied changes from StyleCI

Author: pschocke

README.md

@@ -43,6 +43,9 @@ Next we need to add this token to our Laravel configurations. Create a new Faceb
 
     // Optional - Omit this if you want to use default version.
     'version' => env('FACEBOOK_GRAPH_API_VERSION', '4.0')
+    
+    // Optional - If set, the appsecret_proof will be send to verify your page-token
+    'app-secret' => env('FACEBOOK_APP_SECRET', '')
 ],
 ...
 ```

src/Facebook.php

@@ -20,6 +20,9 @@ class Facebook
     /** @var string|null Page Token. */
     protected $token;
 
+    /** @var string|null App Secret */
+    protected $secret;
+
     /** @var string Default Graph API Version */
     protected $graphApiVersion = '4.0';
 
@@ -48,6 +51,20 @@ public function setGraphApiVersion($graphApiVersion): self
         return $this;
     }
 
+    /**
+     * Set App Secret to generate appsecret_proof.
+     *
+     * @param string $secret
+     *
+     * @return Facebook
+     */
+    public function setSecret($secret = null): self
+    {
+        $this->secret = $secret;
+
+        return $this;
+    }
+
     /**
      * Get HttpClient.
      *
@@ -117,6 +134,12 @@ protected function api(string $endpoint, array $options, $method = 'GET')
 
         $url = "https://graph.facebook.com/v{$this->graphApiVersion}/{$endpoint}?access_token={$this->token}";
 
+        if ($this->secret) {
+            $appsecret_proof = hash_hmac('sha256', $this->token, $this->secret);
+
+            $url .= "&appsecret_proof={$appsecret_proof}";
+        }
+
         try {
             return $this->httpClient()->request($method, $url, $options);
         } catch (ClientException $exception) {

src/FacebookServiceProvider.php

@@ -19,7 +19,9 @@ public function boot()
             ->give(static function () {
                 $facebook = new Facebook(config('services.facebook.page-token'));
 
-                return $facebook->setGraphApiVersion(config('services.facebook.version', '4.0'));
+                return $facebook
+                    ->setGraphApiVersion(config('services.facebook.version', '4.0'))
+                    ->setSecret(config('services.facebook.app-secret'));
             });
     }
 }