Signed Offers & Receipts

npm install @x402/express @x402/extensions @x402/evm @x402/core viem

# Wallet address that receives payments
EVM_ADDRESS=0xYourPaymentWalletAddress

# Private key for signing offers and receipts (EIP-712)
# This should be a DEDICATED SIGNING KEY, not the payment wallet's key
# For production deployments, do not store private keys in an environment variable
SIGNING_PRIVATE_KEY=0xYourDedicatedSigningPrivateKey

# x402 facilitator URL
FACILITATOR_URL=https://facilitator.x402.org

import { config } from "dotenv";
import express from "express";
import { paymentMiddleware, x402ResourceServer } from "@x402/express";
import { ExactEvmScheme } from "@x402/evm/exact/server";
import { HTTPFacilitatorClient } from "@x402/core/server";
import {
  createOfferReceiptExtension,
  createEIP712OfferReceiptIssuer,
  declareOfferReceiptExtension,
} from "@x402/extensions/offer-receipt";
import { privateKeyToAccount } from "viem/accounts";

config();

const evmAddress = process.env.EVM_ADDRESS as `0x${string}`;
const signingPrivateKey = process.env.SIGNING_PRIVATE_KEY as `0x${string}`; // not for production
const facilitatorUrl = process.env.FACILITATOR_URL!;

// Create EIP-712 signer from the dedicated signing key
const signingAccount = privateKeyToAccount(signingPrivateKey);
const kid = `did:pkh:eip155:1:${signingAccount.address}#key-1`;

const offerReceiptIssuer = createEIP712OfferReceiptIssuer(
  kid,
  signingAccount.signTypedData.bind(signingAccount),
);

// Set up the resource server with the extension
const facilitatorClient = new HTTPFacilitatorClient({ url: facilitatorUrl });
const resourceServer = new x402ResourceServer(facilitatorClient)
  .register("eip155:84532", new ExactEvmScheme())
  .registerExtension(createOfferReceiptExtension(offerReceiptIssuer));

const app = express();

// Configure payment routes with offer-receipt enabled
app.use(
  paymentMiddleware(
    {
      "GET /api/data": {
        accepts: [
          {
            scheme: "exact",
            price: "$0.001",
            network: "eip155:84532",
            payTo: evmAddress, // Payment goes here (different from signing key)
          },
        ],
        description: "Premium data endpoint",
        mimeType: "application/json",
        extensions: {
          ...declareOfferReceiptExtension({ includeTxHash: false }),
        },
      },
    },
    resourceServer,
  ),
);

// Your business logic — unchanged
app.get("/api/data", (req, res) => {
  res.json({ data: "your premium content" });
});

app.listen(4021, () => {
  console.log("Server listening on http://localhost:4021");
  console.log("Offer-receipt extension enabled (EIP-712)");
});

EVM_ADDRESS=0xYourPaymentWalletAddress
FACILITATOR_URL=https://facilitator.x402.org

# Base64-encoded PKCS#8 private key (EC P-256)
# For production deployments, do not store private keys in an environment variable
SIGNING_PRIVATE_KEY=base64EncodedPrivateKey

# Your server's domain (URL-encoded for did:web)
# e.g., "api.example.com" or "localhost%3A4021" for local dev
SERVER_DOMAIN=api.example.com

import * as crypto from "crypto";
import {
  createOfferReceiptExtension,
  createJWSOfferReceiptIssuer,
  declareOfferReceiptExtension,
  type JWSSigner,
} from "@x402/extensions/offer-receipt";

const serverDomain = process.env.SERVER_DOMAIN!;
const signingPrivateKey = process.env.SIGNING_PRIVATE_KEY!; // not for production

const did = `did:web:${serverDomain}`;
const kid = `${did}#key-1`;

// Create JWS signer from PKCS#8 private key
const privateKeyPem = `-----BEGIN PRIVATE KEY-----\n${signingPrivateKey}\n-----END PRIVATE KEY-----`;
const keyObject = crypto.createPrivateKey(privateKeyPem);
const publicKeyJwk = keyObject.export({ format: "jwk" });
delete (publicKeyJwk as Record<string, unknown>).d; // Remove private component

const jwsSigner: JWSSigner = {
  kid,
  format: "jws",
  algorithm: "ES256",
  async sign(payload: Uint8Array): Promise<string> {
    const sign = crypto.createSign("SHA256");
    sign.update(payload);
    const signature = sign.sign(privateKeyPem);
    return Buffer.from(derToRaw(signature)).toString("base64url");
  },
};

const offerReceiptIssuer = createJWSOfferReceiptIssuer(kid, jwsSigner);

// Register with x402ResourceServer the same way as the EIP-712 example:
// resourceServer.registerExtension(createOfferReceiptExtension(offerReceiptIssuer));

app.get("/.well-known/did.json", (req, res) => {
  res.setHeader("Content-Type", "application/did+json");
  res.json({
    "@context": [
      "https://www.w3.org/ns/did/v1",
      "https://w3id.org/security/suites/jws-2020/v1",
    ],
    id: did,
    verificationMethod: [
      {
        id: kid,
        type: "JsonWebKey2020",
        controller: did,
        publicKeyJwk,
      },
    ],
    assertionMethod: [kid],
  });
});

declareOfferReceiptExtension({
  // Include the blockchain transaction hash in receipts.
  // Default: false (for privacy — the payer address is still included).
  // Set to true if verifiability is more important than privacy.
  includeTxHash: false,

  // How long offers remain valid, in seconds.
  // Default: 300 (5 minutes). Falls back to the route's maxTimeoutSeconds.
  offerValiditySeconds: 300,
});

import {
  createOfferReceiptExtension,
  createEIP712OfferReceiptIssuer,
} from "@x402/extensions/offer-receipt";

// The provider's SDK gives you a signTypedData function
// that calls their API — the private key never leaves their infrastructure
const signerAddress = "0xYourServerWalletAddress";
const kid = `did:pkh:eip155:1:${signerAddress}#key-1`;

const offerReceiptIssuer = createEIP712OfferReceiptIssuer(kid, async (params) => {
  // Call your wallet provider's signing API
  return await yourWalletProvider.signTypedData({
    domain: params.domain,
    types: params.types,
    primaryType: params.primaryType,
    message: params.message,
  });
});

// Register as usual
resourceServer.registerExtension(createOfferReceiptExtension(offerReceiptIssuer));

import {
  extractOffersFromPaymentRequired,
  decodeSignedOffers,
  verifyOfferSignatureJWS,
  verifyOfferSignatureEIP712,
  isJWSSignedOffer,
} from "@x402/extensions/offer-receipt";

// After receiving a 402 response:
const paymentRequiredBody = await response.json();
const signedOffers = extractOffersFromPaymentRequired(paymentRequiredBody);
const decodedOffers = decodeSignedOffers(signedOffers);

// Verify an offer signature
for (const decoded of decodedOffers) {
  if (isJWSSignedOffer(decoded.signedOffer)) {
    await verifyOfferSignatureJWS(decoded.signedOffer);
  } else {
    await verifyOfferSignatureEIP712(decoded.signedOffer);
  }
}

import {
  extractReceiptFromResponse,
  verifyReceiptMatchesOffer,
  verifyReceiptSignatureJWS,
  verifyReceiptSignatureEIP712,
  isJWSSignedReceipt,
} from "@x402/extensions/offer-receipt";

// After a successful payment response:
const signedReceipt = extractReceiptFromResponse(paidResponse);

// Verify the receipt signature
if (isJWSSignedReceipt(signedReceipt)) {
  await verifyReceiptSignatureJWS(signedReceipt);
} else {
  await verifyReceiptSignatureEIP712(signedReceipt);
}

// Verify the receipt matches the offer you accepted
const verified = verifyReceiptMatchesOffer(
  signedReceipt,
  selectedOffer,
  [yourWalletAddress],
);