backpack for laravel extends AuthenticatesUser method

I'm using Laravel's backpack Crud, I need to change the line of code located in vendor/laravel/src/illuminate/foundation/Auth/AuthenticatesUsers.php

from :

 public function username()
 {   
     return 'email';
 }

to :

 /**
 * Get the login username to be used by the controller.
 *
 * @return string
 */
public function username()
{   
        return 'username';
}

I tried to extend it on my controllers/admin/auth/logincontroller.php with no success, where or how should i do for it to work?

via Chebli Mohamed