Closed-loop authentication, as applied to computer network communication, refers to a mechanism whereby one party verifies the purported identity of another party by requiring them to supply a copy of a token transmitted to the canonical or trusted point of contact for that identity.
A problem associated with this variation is the tendency of a naïve or inexperienced user to click on a URL if an email encourages them to do so.
This may be because the nature of the relationship between the user and the website is one that holds some long-term value for one or both parties (enough to justify the increased effort and decreased reliability of the registration process.)
It is also used in some cases by websites attempting to impede programmatic registration as a prelude to spamming or other abusive activities.
It is not, however, incompatible with anonymity, if combined with a pseudonymity system in which the authenticated party has adequate confidence.