Function: get_user_by_email

It seems to be more and more common to see sites that allow users to log in with their username or email address.

Here’s how to add that ability to WordPress

//remove_filter('authenticate', 'wp_authenticate_username_password', 20, 3);
add_filter('authenticate', 'wp_authenticate_username_password_redux', 20, 3);
function wp_authenticate_username_password_redux( $user, $username, $password ) {
    if ( is_email( $username ) ) {
        $user_obj = get_user_by_email( $username );
        if ( $user_obj ) $username = $user_obj->user_login;
    }
    return wp_authenticate_username_password( $user, $username, $password );
}

* works with or without the remove_filter line.