Sign in with Shop to check out with your saved addresses and Shop wallet, and to send a buyer-linked token with searches for personalization.
Sign-in uses Shop's device flow: you get a short code, approve it on Shop in another tab, and this panel picks the token up. It runs through this store's app proxy, so the browser never touches a client secret and the buyer token goes upstream from the server.
Already have a catalog token — from shop auth or your own exchange? Paste it here. Same result: it goes out as Authorization: Bearer …. Stored for this tab only.