security.yml

#app/config/security.yml

security:
    providers:
        fos_userbundle:
            id:        my.custom.user_provider.username_email

service.xml

<!-- YourBundle/resource/config/service.xml -->
<?xml version="1.0" encoding="UTF-8"?>

<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">
    <services>
        <service id="my.custom.user_provider.username_email" class="My\Custom\User\UserProvider" public="false">
            <argument type="service" id="fos_user.user_manager" />
        </service>        
    </services>
</container>

UserProvider.php

<?php
namespace My\Custom\User;
use FOS\UserBundle\Security;
use Symfony\Component\Security\Core\User\UserInterface;

class UserProvider extends EmailUserProvider 
{
    public function refreshUser(UserInterface $user)
    {
        return $user;
    }
}