Use email instead of loginname in WP

function.php

<?php

/*
*
*
* Usar mails para el login en vez de usuarios
*
*
*/
remove_filter( 'authenticate', 'wp_authenticate_username_password', 20, 3 );
add_filter( 'authenticate', 'fb_authenticate_username_password', 20, 3 );
function fb_authenticate_username_password( $user, $username, $password ) {
    // If an email address is entered in the username box, 
    // then look up the matching username and authenticate as per normal, using that.
    if ( ! empty( $username ) )
        $user = get_user_by( 'email', $username );

    if ( isset( $user->user_login, $user ) )
        $username = $user->user_login;

    // using the username found when looking up via email
    return wp_authenticate_username_password( NULL, $username, $password );
}