express-server

PrivAgent Express Server — Privacy Paywall

Add a privacy-preserving paywall to any Express API endpoint.

Setup

npm install privagent-sdk ethers express

Usage

import express from 'express';
import { privAgentPaywallV4 } from 'privagent-sdk/x402';
import { JsonRpcProvider, Wallet } from 'ethers';

const app = express();
const signer = new Wallet(process.env.PRIVATE_KEY!, new JsonRpcProvider(process.env.BASE_SEPOLIA_RPC));

// Add privacy paywall to premium endpoints
app.get('/api/premium', privAgentPaywallV4({
  price: 1_000000n,  // 1 USDC
  signer,
  poolAddress: '0x8F1ae8209156C22dFD972352A415880040fB0b0c',
}), (req, res) => {
  res.json({ data: 'premium content' });
});

app.listen(3001);

How It Works

1. Client requests /api/premium
2. Middleware returns 402 with zk-exact-v2 payment requirements
3. Client generates JoinSplit ZK proof and retries with Payment header
4. Middleware decrypts the encrypted note to verify payment amount
5. Middleware calls transact() on-chain
6. Request proceeds to your handler