algovoi-x402-receipt-adapter

Turn an x402 payment into an offline verifiable receipt.

x402 proves a payment happened with a single txHash in the PAYMENT-RESPONSE header. The amount and currency live in the upstream PAYMENT-REQUIRED header, nothing binds the two together, and verifying the payment means hitting the chain. There is no receipt.

This adapter takes both headers and produces a settlement_attestation_v1: a JSON object canonicalised under RFC 8785 (JCS) and content addressed with SHA-256. Any party recomputes the reference and confirms the bytes with a JSON parser, JCS, and SHA-256 alone. No chain call, no issuer service, no account.

What it produces

PAYMENT-REQUIRED   ->  maxAmountRequired, asset, payTo, network
PAYMENT-RESPONSE   ->  txHash, networkId, payer, success
                          |
      x402_payment_ref = sha256(JCS({txHash, networkId, payer,
                                     amount, currency, settled_at_ms}))
                          |
      settlement_attestation_v1   (settlement_ref content addresses it)

• x402_payment_ref binds the response txHash to the requested amount and currency plus an injected timestamp, so a txHash can no longer be re-bound to a different amount.
• settlement_ref is sha256: + SHA-256(JCS(attestation)), the content address of the whole receipt.

Install

pip install algovoi-x402-receipt-adapter

Use

from algovoi_x402_receipt_adapter import build_x402_settlement_attestation

payment_required = {
    "scheme": "exact",
    "network": "base",
    "maxAmountRequired": "1000000",   # atomic minor units (USDC, 6dp)
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "payTo": "0x7D01d268636c835d9E56164A24A9587D82B8B186",
}
payment_response = {
    "success": True,
    "txHash": "0x7ae7b2750c6de4507af6a06305e403b82a31d1090d6330f57d83707800ac6acb",
    "networkId": "base",
    "payer": "0x1234...",
}

result = build_x402_settlement_attestation(
    payment_required,
    payment_response,
    settled_at_ms=1751472000000,
    provider_did="did:web:your-service.example",
    jurisdiction_flags=["UK", "EU"],
)

result["settlement_ref"]      # "sha256:..."
result["x402_payment_ref"]    # "sha256:..."
result["attestation"]         # the 8-field settlement_attestation_v1

Either header may be passed as a decoded dict or as the raw base64(JSON) header value. The settlement fields follow the x402 Foundation SettleResponse model (transaction, network, payer); the legacy names txHash and networkId are accepted as aliases, so the adapter reads a PAYMENT-RESPONSE header regardless of which naming a gateway emits.

Verify offline

from algovoi_x402_receipt_adapter import verify_settlement_ref

verify_settlement_ref(result["attestation"], result["settlement_ref"])  # True

The check is pure and deterministic: sha256: + SHA-256(JCS(attestation)). Recompute it in any language with an RFC 8785 canonicaliser and a SHA-256, and the reference matches byte for byte.

Determinism

The adapter injects no clock and asserts no identity of its own: settled_at_ms and provider_did are explicit arguments. The same headers with the same arguments always produce the same references. A frozen conformance vector ships with the source tests.

Fields

settlement_attestation_v1 carries exactly eight fields, sorted lexicographically by JCS:

Three ways to capture

All three yield the same settlement_attestation_v1, and to_keystone_binding binds any of them into the Keystone. All settlement fields accept the x402 Foundation SettleResponse names (transaction, network, payer), with the legacy txHash / networkId accepted as aliases.

A. Facilitator side

from algovoi_x402_receipt_adapter import receipt_from_settle

result = receipt_from_settle(
    payment_requirements,          # x402 PaymentRequirements (maxAmountRequired, asset, payTo)
    settle_response,               # your facilitator's SettleResponse (success, transaction, network, payer, amount)
    settled_at_ms=1751472000000,
    provider_did="did:web:your-facilitator.example",
    keystone_context={"action_ref": "…", "transition_hash": "…", "retention_chain_ref": "sha256:…"},
)
result["settlement_ref"]     # same value option B or C would produce
result["confirmed_amount"]   # actual settled amount (SettleResponse.amount when present)

As the facilitator you settled the payment, so the result is trusted by default; pass reverify for an optional on-chain check.

B. Secure capture, origin side (recommended for managed gateways)

A settlement gateway (for example Cloudflare, which returns the result inline in a PAYMENT-RESPONSE header and exposes no settlement API or webhook) hands you the two headers on the paid request. Do not trust them at face value: a forged or replayed PAYMENT-RESPONSE would otherwise mint a false receipt. capture_x402_settlement closes that hole by re-verifying the transaction on chain before it builds or binds anything:

from algovoi_x402_receipt_adapter import capture_x402_settlement

def verify(network_id, tx_id, expected_receiver, expected_amount_minor, expected_asset):
    # wire to the AlgoVoi facilitator POST /verify, or an in-process verifier.
    # MUST return {"verified": bool, "confirmed_amount": int}.
    ...

result = capture_x402_settlement(
    payment_required, payment_response,
    verify=verify,
    settled_at_ms=1751472000000,
    provider_did="did:web:your-service.example",
    keystone_context={"action_ref": "…", "transition_hash": "…", "retention_chain_ref": "sha256:…"},
    already_bound=lambda tx: store.get(tx),   # idempotency on txHash
)
result["binding_ref"]        # the payment, verified and bound into the Keystone
result["confirmed_amount"]   # the actual on-chain amount recorded

Security properties: fail closed (no on-chain confirmation, no binding), unforgeable (binding requires a real payment to your payTo), replay safe (idempotent on txHash). The attestation records the confirmed on-chain amount, not the quoted maximum. Run this at your origin, ideally behind authenticated origin pull so a spoofed request cannot reach it in the first place.

Bind it into the Keystone

The settlement this adapter produces can be bound into the AlgoVoi Keystone accountability chain, so a payment is tied to the verified agent action it settled. This uses the published algovoi-substrate binding primitive and introduces no new hashing:

from algovoi_x402_receipt_adapter import (
    build_x402_settlement_attestation, to_keystone_binding,
)

result = build_x402_settlement_attestation(
    payment_required, payment_response,
    settled_at_ms=1751472000000, provider_did="did:web:your-service.example",
)

binding_ref = to_keystone_binding(
    result,
    action_ref="…",            # the verified agent action (bare 64-char hex)
    transition_hash="…",       # the COMMITTED lifecycle transition (bare hex)
    retention_chain_ref="sha256:…",  # tamper-evident chain position
)

binding_ref = sha256(JCS({ action_ref, transition_hash,
                           settlement_ref, retention_chain_ref }))

binding_ref proves which action the payment settled: changing the settlement, the action, the transition, or the chain position changes it. Recompute it offline with a JCS canonicaliser and SHA-256, the same as settlement_ref.

Making the payment a Keystone execution step (recipe)

To place the payment as the execution step of a full Keystone chain (passport -> mandate -> policy -> decision -> execution -> trust_query), map the settlement into an execution_ref record with the algovoi-execution-ref primitive and carry the settlement attestation as that step's evidence:

from algovoi_execution_ref import execution_ref   # optional extra dependency

exec_ref = execution_ref(
    decision_ref=decision_ref,                     # the ALLOW that authorised the spend
    action_type="payment.settle",
    scope=f"{result['attestation']['settlement_chain']}:{payment_response['txHash']}",
    outcome="COMMITTED",
    executed_at_ms=1751472000000,
)

This adapter does not depend on algovoi-execution-ref; the recipe is opt-in so the package stays lean.

Networks

networkId maps to the AlgoVoi settlement_chain form (for example base maps to ethereum:8453, base-sepolia to ethereum:84532, solana-devnet to solana:devnet). Any eip155:<chainId> is mapped automatically. Pass network_map={...} or settlement_chain=... to override, or strict=False to pass an unknown id through unchanged.

Licence

Apache License 2.0. See LICENSE and NOTICE.