Missing Authentication for Critical Function (CWE-306) in the checkout session lookup handler (src/app/api/stripe/checkout_sessions/route.ts), exposed at GET /api/stripe/checkout_sessions, in MarcosCamara01 Ecommerce Template before commit 91e273c allows a remote, unauthenticated attacker holding a valid Stripe Checkout Session id (cs_...) to retrieve the full session object, including the buyer's name, email, phone, billing address, amount paid and internal userId, because the GET handler calls stripe.checkout.sessions.retrieve() and returns the result without checking for an authenticated session or session ownership. Sibling endpoints such as POST /api/stripe/payment already enforced authentication via auth.api.getSession(); this endpoint had no access control whatsoever. The session_id is exposed in the buyer's own browser URL after payment (success_url = /result?session_id={CHECKOUT_SESSION_ID}), so it leaks through Referer headers, analytics tools, server access logs and shared-machine browser history, resulting in disclosure of the buyer's personal data to an unauthenticated actor.