Protocol

AP2

Agent Payments Protocol

The merchant-signed checkout carries the ATR hash, and the buyer’s Checkout Mandate commits to that checkout. Source: lcp docs: agentic checkouts⁠ (opens in a new tab) The Agentic Transaction Record (ATR) is one record of exactly what was agreed, for one transaction. Its ATR hash, the ATR’s fingerprint, is the proof bound to the transaction: change one byte of the ATR and it no longer matches. Source: lcp docs: the ATR⁠ (opens in a new tab) · Source: lcp docs: the ATR hash⁠ (opens in a new tab)

AP2, the Agent Payments Protocol, was originated by Google and is now governed by the FIDO Alliance. Source: LCP §C.5⁠ (opens in a new tab) Integra is not affiliated; we read their published interfaces.

lcp docs: agentic checkouts⁠ (opens in a new tab) · lcp docs: the ATR⁠ (opens in a new tab) · lcp docs: the ATR hash⁠ (opens in a new tab) · LCP §C.5⁠ (opens in a new tab)

The protocol’s own site⁠The standard’s illustration of this protocol (LCP §C.5)⁠

AP2

Payment mandates

The merchant’s signed checkout: The ATR hash, as its legalContext.
The buyer’s Checkout Mandate: Commits to that checkout through its hash.

Run an agentic transaction over AP2 now

A real transaction between Integra-managed agents on a test network, then its proof: the agreed terms, bound to the payment.

Loading the demonstrations…

These are real transactions between Integra-managed agents, using testnet funds. Transactions are settled at 1/10,000th of their stated value, for demonstration purposes.

What it is

AP2 is an open protocol for agent-driven payments, built on mandates: verifiable digital credentials that capture what a user authorized. Source: LCP §C.5⁠ (opens in a new tab)

AP2 defines no transport: the protocol that carries the mandate does. Source: LCP §C.5⁠ (opens in a new tab)

LCP §C.5⁠ (opens in a new tab)

Where the ATR hash rides

The checkout the merchant signs carries the ATR hash, and the buyer’s mandate commits to that checkout.

Exhibit Where it rides, in the protocol’s and the package’s terms

The standard

A reference written into an open mandate’s constraints would fail validation: that array is a closed set, and a new constraint type is registered through the FIDO Alliance working groups that govern AP2. Source: LCP §C.5⁠ (opens in a new tab)

The package

The merchant signs a checkout_jwt whose payload carries the ATR hash as its legalContext member; the buyer’s closed Checkout Mandate commits to that JWT through checkout_hash, the SHA-256 of the JWT. Source: lcp docs: agentic checkouts⁠ (opens in a new tab)

The seller reads the ATR hash from inside the mandate. AP2 has the credential provider verify the Payment Mandate before a payment credential issues; the pairing’s record states which signatures the seller did and did not check. Source: lcp docs: pairings reference⁠ (opens in a new tab)

What a payment through it proves

Each pairing’s record states what a payment through it shows, and what it does not, in the package’s own words. These are read from the package when the site is built. Source: lcp docs: pairings reference⁠ (opens in a new tab)

On this pairing, the buyer’s signature covers the ATR hash, the payment does not leave a public proof of it, and no one can read it back from the chain alone. Source: lcp docs: pairings reference⁠ (opens in a new tab)

Switch to Technical to see each pairing, and the sentence its record states about what a payment through it proves.

lcp docs: pairings reference⁠ (opens in a new tab)

Exhibit Each pairing’s record

The package

Pattern: Opaque Challenge (LCP §8.3.4)⁠ (opens in a new tab)
What a payment through it proves: Before this payment, the buyer signed and paid an agreement transaction carrying this ATR's hash on <network>, recorded in <transaction>. The buyer's closed AP2 Checkout Mandate carries checkout_hash, the SHA-256 of the checkout JWT presented beside it, and that JWT's payload carries this ATR's hash as its legalContext member. The mandate's signer is the user's trusted surface, or the agent under the user's open mandate, presented before it in a chain. The seller did not verify that signature, the open mandate's signature or delegation to the agent's key (cnf), or the chain's link between them: AP2 has the Credential Provider verify the Payment Mandate, whose transaction_id is the same hash, before a payment credential issues. The seller reported the payment. This does not show that amount, payee or timing match the ATR's content.
LCP profile: ap2/checkout-mandate⁠ (opens in a new tab)

Where a sentence names <network> and <transaction>, the pairing’s record fills them in: they name the agreement payment the buyer made first. Source: lcp docs: pairings reference⁠ (opens in a new tab) · Source: lcp docs: the agreement URL⁠ (opens in a new tab)

The rails it settles on

A checkout through this protocol is paid by the provider the checkout names, so it lists no rail of its own.

Ready to see your own agreements proved?

Tell us what you sell, buy or carry, and we will show you where the agreement rides in it.

Integra Binder, hosted by Integra, does the seller’s side of each agreement and is free on test networks, with test-network USDC.

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