It seems like you could interpret the line "You can’t charge a fee, require the recipient to give you any personally identifying information beyond an email address, or make the recipient take any step other than sending a reply email or visiting a single page on an Internet website as a condition for honoring an opt-out request." to mean that you can't require the user to log in (as that would give you more information about them than just their email address, or because requires visiting more than one page [login and then unregister]).