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AP2 (Agent Payments Protocol)

JACS can export the merchant/business-authorization artifact of the UCP AP2-Mandates extension (dated spec revision 2026-01-23) as a detached ES256 JWS, signed with the agent's ecosystem_signing compatibility key.

Scope is deliberately narrow:

  • Exported role: merchant/business authorization only. User-side AP2 Checkout Mandates are SD-JWT-VC and are not produced by JACS — this is not full AP2 conformance, and the docs do not claim it.
  • Outgoing only. JACS does not verify incoming AP2 mandates.
  • CLI + binding only. There is no MCP tool for this export.

Wire format (pinned)

  • Protected header: exactly {"alg":"ES256","kid":"<compat-key kid>"} — no typ, no RFC 7797 b64:false, no crit.
  • Detached compact serialization: <BASE64URL(header)>..<BASE64URL(signature)>.
  • Signing input: BASE64URL(header) + "." + BASE64URL(JCS(payload)), where the payload is the checkout object excluding the ap2 field, canonicalized per RFC 8785 (JCS).

The exporter validates its input against the named schema jacs/schemas/compatibility/ap2-mandate/v1/ap2-mandate.schema.json and rejects anything that does not conform — typed input is a schema check, not a naming convention.

The schema is deliberately open (additionalProperties: true) to match UCP checkout extensibility: extra checkout fields beyond the required core are signed as-is, so relying parties must not assume JACS validated anything beyond the schema's required core fields. Operators granting the ap2-mandate scope are authorizing signatures over extensible checkout payloads.

Usage

The ap2-mandate binding scope is a content scope: it is never auto-issued. Grant it explicitly first (this requires the native root's signature):

jacs agent issue-compat-binding \
  --scopes jwks,did,a2a-agent-card,w3c-agent-identity,ap2-mandate

# inline JSON, a file path, or '-' for stdin all work:
jacs ap2 export-mandate --input checkout.json > export.json
cat checkout.json | jacs ap2 export-mandate --input - > export.json

The export carries the detached JWS, the checkout with ap2.merchant_authorization filled in, and the binding reference as a content hash.

Verification

Any stock JOSE verifier can check the ES256 signature against the agent's JWKS — see the committed reference verifier:

jacs agent export-jwks > jwks.json
npm install jose canonicalize
node scripts/smoke/verify_ap2_jws.mjs export.json jwks.json

Classical verification is not native-root trust. The ES256 check proves possession of the compatibility key only. To trace the mandate to the agent's native root, a JACS-aware relying party additionally verifies the native-root-signed compatibility key binding (jacs agent export-compat-binding) whose content hash the export references. Native JACS documents are never touched by this export — signing a mandate does not create or modify any jacsSignature.