x402 Payments

npm install @xentfi/x402-facilitator-sdk

import type { PaymentRequirement } from "@xentfi/x402-facilitator-sdk";

const requirement: PaymentRequirement = {
  scheme: "eip3009",
  network: "base-mainnet",
  blockchainId: "2fad7eb1-4405-4400-af4f-2b37401a6bd6",
  assetId: "b3d641bb-f28f-4d1f-b89c-a504ad51f453",
  maxAmountRequired: "1.00",
  payTo: "0xYourWalletAddress",
  resource: "GET /premium-report",
  maxTimeoutSeconds: 3600,
};

import Fastify from "fastify";
import { X402FacilitatorClient } from "@xentfi/x402-facilitator-sdk";
import type { PaymentPayload, PaymentRequirement } from "@xentfi/x402-facilitator-sdk";

const facilitator = new X402FacilitatorClient({
  apiKey: process.env.WAAS_API_KEY!,
  orgId: process.env.WAAS_ORG_ID!,
});

const app = Fastify();

app.get("/premium-report", async (req, reply) => {
  const proofHeader = req.headers["x-payment"];

  if (!proofHeader) {
    // No payment attached yet — issue the 402 challenge.
    return reply.status(402).send({ x402Version: 1, accepts: [requirement] });
  }

  const paymentPayload: PaymentPayload = JSON.parse(
    Buffer.from(proofHeader as string, "base64").toString("utf8"),
  );

  try {
    // Throws on invalid signature, expired authorization, wrong amount, etc.
    await facilitator.verify(paymentPayload, requirement);

    // Submits the TransferWithAuthorization on-chain via your WAAS relayer wallet.
    const settlement = await facilitator.settle(paymentPayload, requirement);

    return { report: "... the actual paid content ...", txHash: settlement.txHash };
  } catch (error) {
    return reply.status(402).send({
      x402Version: 1,
      accepts: [requirement],
      error: (error as Error).message,
    });
  }
});

app.listen({ port: 3000 });

import { privateKeyToAccount } from "viem/accounts";
import { signEip3009Authorization } from "@xentfi/x402-facilitator-sdk";
import type { Eip3009TokenDomain, X402Challenge } from "@xentfi/x402-facilitator-sdk";

const account = privateKeyToAccount(process.env.PAYER_PRIVATE_KEY! as `0x${string}`);

const domain: Eip3009TokenDomain = {
  chainId: 8453,
  tokenAddress: "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  tokenName: "USD Coin",
  tokenVersion: "2",
  tokenDecimals: 6,
};

async function main() {
  const url = "https://merchant.example.com/premium-report";

  // 1. First request — expect a 402 challenge.
  const firstResponse = await fetch(url);
  if (firstResponse.status !== 402) return console.log(await firstResponse.json());

  const challenge = (await firstResponse.json()) as X402Challenge;
  const requirement = challenge.accepts.find((r) => r.scheme === "eip3009");
  if (!requirement) throw new Error("Server doesn't support the 'eip3009' scheme");

  // 2. Sign a real EIP-3009 authorization for the required amount.
  const paymentPayload = await signEip3009Authorization({
    account,
    to: requirement.payTo,
    amount: requirement.maxAmountRequired,
    domain,
  });

  // 3. Retry with the signed payment attached.
  const header = Buffer.from(JSON.stringify(paymentPayload)).toString("base64");
  const secondResponse = await fetch(url, { headers: { "X-PAYMENT": header } });
  console.log(secondResponse.status, await secondResponse.json());
}

main();

function signEip3009Authorization(
  params: SignExactAuthorizationParams
): Promise<Eip3009SchemePayload>;