@countersign/ap2

@countersign/ap2

Govern AP2 (the Agent Payments Protocol) with Countersign — guard an agent's mandate against policy before it signs the PaymentMandate.

When an agent is about to commit to a merchant-signed Cart/Checkout Mandate — the moment a final amount and payee are known but funds have not moved — route it through Countersign's pre-flight spend guard: parse the mandate → evaluate against one unified policy (per-call caps + payee allowlist + daily metering, fail-closed) → only sign/send the PaymentMandate if allowed. Countersign decides; it never signs a mandate or moves funds.

import { parseAp2, withAp2Guard } from "@countersign/ap2";
import { CountersignClient } from "@countersign/sdk";

const cs = new CountersignClient({ baseUrl, apiKey });

// `mandate` is a merchant-signed AP2 Cart/Checkout Mandate (or a PaymentMandate).
const charge = parseAp2(mandate);                 // normalized: amount (minor units) + currency + payee
if (charge) {
  // Only signs/sends if Countersign allows — a rogue or over-budget agent never pays.
  await withAp2Guard(cs, agentId, charge, (c) => signAndSendPaymentMandate(c));
}

• parseAp2(mandate) — normalize an AP2 mandate to a single charge. Handles both spec generations: Gen-1 (W3C-PaymentRequest, float major units) and Gen-2/v0.2 (SD-JWT VC, int minor units); the amount is always returned as an integer minor-unit string.
• guardAp2(api, agentId, charge) — ask Countersign: allow / deny / needs_approval.
• withAp2Guard(api, agentId, charge, pay) — evaluate, then run pay only on allow; throws Ap2Denied otherwise.

AP2 has no official npm/TS SDK yet and the spec (v0.2) is still evolving — the mandate types here are transcribed from the reference schemas. Pairs with @countersign/sdk, @countersign/mcp, and @countersign/x402.

Apache-2.0.