The UserInterface interface - http://www.symfonycentral.com/securing-your-web-application-with-symfony.html

UserInterface.php

<?php 
interface UserInterface
{
    /**
     * Returns an array of strings, where each string is a role that this user has.
     *
     * @return Role[] An array containing the roles this user has
     */
    function getRoles();

    /**
     * Return the salted and hashed password for this user.
     *
     * @return string The password
     */
    function getPassword();

    /**
     * Return the "salt" value used to save this user's password.
     *
     * @return bool|string The salt
     */
    function getSalt();

    /**
     * Return the username of this user.
     *
     * @return string The username
     */
    function getUsername();

    /**
     * Remove sensitive information from the user object.
     *
     * @return void
     */
    function eraseCredentials();

    /**
     * Given another User object, return true if the provided $user is equivalent to this one.
     *
     * @param UserInterface $user
     * @return Boolean
     */
    function equals(UserInterface $user);
}