Added OAuth functionalities

- Added Mercado Pago OAuth functionalities
- Fixed proccess_causes method

src/MercadoPago/Entities/OAuth.php

@@ -0,0 +1,82 @@
+<?php
+namespace MercadoPago;
+use MercadoPago\Annotation\RestMethod;
+use MercadoPago\Annotation\Attribute; 
+
+/**
+ * @RestMethod(resource="/oauth/token", method="create")
+ */
+
+class OAuth extends Entity
+{
+   /**
+     * @Attribute()
+     */
+    protected $client_secret;
+    /**
+     * @Attribute()
+     */
+    protected $grant_type;
+    /**
+     * @Attribute()
+     */
+    protected $code;
+    /**
+     * @Attribute()
+     */
+    protected $redirect_uri;
+
+    /**
+     * @Attribute()
+     */
+    protected $access_token;
+    /**
+     * @Attribute()
+     */
+    protected $public_key;
+    /**
+     * @Attribute()
+     */
+    protected $refresh_token;
+    /**
+     * @Attribute()
+     */
+    protected $live_mode;
+    /**
+     * @Attribute()
+     */
+    protected $user_id;
+    /**
+     * @Attribute()
+     */
+    protected $token_type;
+    /**
+     * @Attribute()
+     */
+    protected $expires_in;
+    /**
+     * @Attribute()
+     */
+    protected $scope;
+
+    public function getAuthorizationURL($app_id, $redirect_uri){
+      return "https://auth.mercadopago.com.br/authorization?client_id=${app_id}&response_type=code&platform_id=mp&redirect_uri=${redirect_uri}";
+    }
+
+    public function getOAuthCredentials($authorization_code, $redirect_uri){
+      $this->client_secret = SDK::getAccessToken();
+      $this->grant_type = 'authorization_code';
+      $this->code = $authorization_code;
+      $this->redirect_uri = $redirect_uri;
+
+      return $this->save();
+    }
+
+    public function refreshOAuthCredentials($refresh_token){
+      $this->client_secret = SDK::getAccessToken();
+      $this->grant_type = 'refresh_token';
+      $this->refresh_token = $refresh_token;
+
+      return $this->save();
+    }
+}

src/MercadoPago/Generic/RecuperableError.php

@@ -24,11 +24,15 @@ public function add_cause($code, $description) {
     }
 
     public function proccess_causes($causes){
-        foreach ($causes as $cause){
-            if(is_array($cause) && (!isset($cause['code']) && !isset($cause['description']))){
-                $this->proccess_causes($cause);
-            }else{
-                $this->add_cause($cause['code'], $cause['description']);
+        if(isset($causes['code']) && isset($causes['description'])){
+            $this->add_cause($causes['code'], $causes['description']);
+        }else{
+            foreach ($causes as $cause){
+                if(is_array($cause) && (!isset($cause['code']) && !isset($cause['description']))){
+                    $this->proccess_causes($cause);
+                }else{
+                    $this->add_cause($cause['code'], $cause['description']);
+                }
             }
         }
     }