proof402-middleware

proof402-middleware

x402/HTTP 402 payment middleware for Express, Next.js, and Cloudflare Workers.
Gate any API behind RLUSD micropayments on XRP Ledger via 402Proof.
Sub-millisecond local HMAC verification. Zero API keys. Zero custody.

Install

npm install proof402-middleware

How It Works

• Agent hits your protected route → middleware checks for X-Payment-Token header
• No token (or invalid) → middleware returns HTTP 402 + invoice (pay_to, memo_hex, amount)
• Agent sends RLUSD on XRPL → calls POST /v1/verify on 402Proof → receives signed token
• Agent retries with X-Payment-Token: <token> → verified locally in <1ms → access granted

Token verification is pure HMAC-SHA256 — zero network call, sub-millisecond when tokenSecret is set.

Express

const express = require('express');
const { proof402 } = require('proof402-middleware');

const app = express();

app.use('/api/premium', proof402({
  endpointId:  'your-endpoint-uuid',          // from 402Proof merchant dashboard
  serverUrl:   'https://four02proof.onrender.com',
  tokenSecret: process.env.PROOF402_TOKEN_SECRET, // enables zero-latency local verify
}));

app.get('/api/premium/data', (req, res) => {
  res.json({ data: 'paid content', verified: req.proof402 });
});

Next.js App Router (middleware.ts)

import { proof402Next } from 'proof402-middleware';

export default proof402Next({
  endpointId:  process.env.PROOF402_ENDPOINT_ID!,
  serverUrl:   'https://four02proof.onrender.com',
  tokenSecret: process.env.PROOF402_TOKEN_SECRET,
});

export const config = { matcher: ['/api/premium/:path*'] };

Cloudflare Workers

import { proof402Worker } from 'proof402-middleware';

async function myHandler(request, env, ctx) {
  return new Response(JSON.stringify({ data: 'paid' }), {
    headers: { 'Content-Type': 'application/json' }
  });
}

export default {
  fetch: proof402Worker({
    endpointId:  'your-endpoint-uuid',
    serverUrl:   'https://four02proof.onrender.com',
    tokenSecret: env.PROOF402_TOKEN_SECRET,
    handler:     myHandler,
  })
};

HTTP 402 Response Format

When payment is required, clients receive:

{
  "error": "Payment Required",
  "invoice": {
    "invoice_id": "inv_abc123",
    "pay_to": "rGATEWAY...",
    "memo_hex": "696e765f616263313233",
    "amount": "0.10",
    "asset": "RLUSD",
    "expires_at": 1747616400
  },
  "instructions": {
    "step1": "Send 0.10 RLUSD on XRPL to rGATEWAY...",
    "step2": "Include MemoData: 696e765f... in your XRPL payment",
    "step3": "POST https://four02proof.onrender.com/v1/verify with invoice_id, tx_hash, agent_wallet",
    "step4": "Retry with header: X-Payment-Token: <token>"
  }
}

Response headers also include X-Payment-Address, X-Payment-Amount, X-Invoice-ID, X-Memo-Hex, X-Verify-URL for machine-readable x402 compliance.

Options

Option	Type	Required	Description
endpointId	string	yes	UUID from 402Proof merchant dashboard
serverUrl	string	no	402Proof server URL (default: https://four02proof.onrender.com)
tokenSecret	string	recommended	Same TOKEN_SECRET as your 402Proof server. Enables zero-network local verification.

Environment Variables

PROOF402_ENDPOINT_ID=your-endpoint-uuid
PROOF402_TOKEN_SECRET=your-token-secret   # from 402Proof server env

Register Your Endpoint

• Go to four02proof.onrender.com
• Register as a merchant → create an endpoint → copy the UUID
• Set endpointId in your middleware config
• Set PROOF402_TOKEN_SECRET to the same value as your 402Proof TOKEN_SECRET

Links

• 402Proof Dashboard: https://four02proof.onrender.com
• 402Proof llms.txt: https://four02proof.onrender.com/llms.txt
• SqueezeOS (live example): https://lively-fascination-production-41fa.up.railway.app
• Python SDK: pip install proof402 (see /402proof/middleware/python/)

License

MIT © Script Master Labs