Add correct encoding and the required state param. (#599)

* Add correct encoding and the required state param.

* Set default state when stateless.

* Update TwitterProvider.php

Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: xhezairbey

src/Two/TwitterProvider.php

@@ -28,6 +28,13 @@ class TwitterProvider extends AbstractProvider
      */
     protected $scopeSeparator = ' ';
 
+    /**
+     * The query encoding format.
+     *
+     * @var int
+     */
+    protected $encodingType = PHP_QUERY_RFC3986;
+
     /**
      * {@inheritdoc}
      */
@@ -83,4 +90,18 @@ public function getAccessTokenResponse($code)
 
         return json_decode($response->getBody(), true);
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function getCodeFields($state = null)
+    {
+        $fields = parent::getCodeFields($state);
+
+        if ($this->isStateless()) {
+            $fields['state'] = 'state';
+        }
+
+        return $fields;
+    }
 }