https://github.com/privacycg/nav-tracking-mitigations/pull/2/files#r704161877 asks how we should think of links like publisher.example/unsubscribe?userId=5789rhkdsaf8urfnsd, where the user ID is used to identify the account to unsubscribe, and may or may not be required. (If it's not required, the user would be able to fill out a text input field on the target site to identify the account.)