Facing problem with Facebook CALLBACK_URL

I am trying to implement login with Facebook funtionality. The demo I am referring to is : http://benmarshall.me/facebook-sdk-php-v4/

I am using CodeIgniter 3.0. After the Facebook login process, the callback URL I am getting is in encoded form.

For example:

the URL index.php?/controller/method

is encoded like index.php?%2Fcontroller%2Fmethod&FACEBOOK_TOKEN

and CodeIgniter is not redirecting this controller and I am stuck at the index page.

Any suggestion for how to resolve this. Thanks in advance.