UCP Payment Authentication Extension

Before writing code

Fetch live spec: Web-search site:ucp.dev specification payment extensions authentication and fetch the extension page plus the two action pages (device-data-collection, three-ds-challenge) for the exact action config fields and handshake message names. This extension touches payment security — do not implement it from memory.

Conceptual Architecture

What it does, and what it does not

The extension standardizes the browser-surface interactions a platform may need to process while a payment attempt is underway. It extends the checkout capability with namespace dev.ucp.common.payment.authentication.

It deliberately does not replace EMV 3DS protocol details. UCP carries where the surface lives and when to show it; the 3DS protocol itself remains between the issuer, the network, and the payment handler.

Two actions