aptosmpp — Aptos Payment Method for the Machine Payments Protocol

Aptos adapter for MPP — the open protocol by Tempo + Stripe that lets any HTTP API accept crypto payments from AI agents using HTTP 402. Solana has theirs. Now Aptos does too.

Install

npm install aptosmpp

What it does

Any HTTP API can require payment before serving a response — no signup, no credit card, no subscription. The client (an AI agent or wallet) pays per request in APT or USDC. The server verifies on-chain and returns the resource.

Two modes:

• Charge — one payment per request, settled on-chain immediately
• Session — client deposits once into a Move escrow contract, sends signed vouchers per request, server settles at the end. Thousands of micropayments for the cost of 2 transactions.

Server

import { MppxServer, aptos } from 'aptosmpp/server';

const mppx = MppxServer.create({
  feePayerPrivateKey: process.env.FEE_PAYER_KEY,
  methods: [
    aptos.charge({
      network: 'mainnet',
      recipient: '0xYourAddress',
      assetAddress: '0xbae207659db88bea0cbead6da0c58b8b7a695f65ef13cf2f9de3e61d83d05a7b', // USDC
      tokenStandard: 'fa',
      decimals: 6,
    }),
  ],
});

app.get('/paid', async (req, res) => {
  const result = await mppx.charge({ amount: '1000000', currency: 'USDC' })(req.headers);
  if (result.status === 402) return res.status(402).set(result.headers).json(result.body);
  res.setHeader('Payment-Receipt', result.receiptHeader);
  res.json({ data: 'your payload' });
});

Client

import { MppxClient, aptos } from 'aptosmpp/client';
import { Ed25519PrivateKey, Account } from '@aptos-labs/ts-sdk';

const account = Account.fromPrivateKey({
  privateKey: new Ed25519PrivateKey(process.env.PRIVATE_KEY),
});

const mppx = MppxClient.create({
  methods: [aptos.charge({ signer: account })],
});

// Automatically handles the 402 challenge/response
const response = await mppx.fetch('https://api.example.com/paid-endpoint');

How it works

Client                          Server                    Aptos Node
  │  GET /resource                 │                           │
  ├──────────────────────────────> │                           │
  │                                │                           │
  │  402 + WWW-Authenticate        │                           │
  │ <────────────────────────────  │                           │
  │                                │                           │
  │  Authorization: Payment <tx>   │                           │
  ├──────────────────────────────> │                           │
  │                                │  simulate + broadcast     │
  │                                ├─────────────────────────> │
  │                                │ <───────────────────────  │
  │  200 OK + Payment-Receipt      │                           │
  │ <────────────────────────────  │                           │

Pull mode (default): Client signs but doesn't broadcast. Server verifies, co-signs as fee payer, broadcasts. Client pays zero gas.

Push mode (fallback): Client broadcasts, sends the tx hash to server. Server verifies on-chain.

Payment Channels (Session Mode)

For AI agents making many calls to the same API:

// Server
const server = MppxSessionServer.create({
  methods: [{
    network: 'mainnet',
    recipient: '0xYourAddress',
    channelModuleAddress: '0xYourDeployedContractAddress',
    pricing: { unit: 'request', amountPerUnit: '10000' },
    sessionDefaults: { suggestedDeposit: '10000000', ttlSeconds: 3600 },
  }],
});

// Client
const client = MppxSessionClient.create({
  methods: [{
    signer: account,
    authorizer: new UnboundedAuthorizer(account),
    buildOpenChannelTx: async (params) => { /* submit open_channel, return hash */ },
  }],
});

The client opens a channel once (deposits funds into a Move escrow), then sends signed vouchers per request with no on-chain transaction each time. The server settles the final voucher when done.

Move Contract

The payment channel contract is in move/aptos_channel/. Deploy it once:

cd move/aptos_channel
aptos move publish --profile server --named-addresses aptos_mpp=<your-address>
aptos move run --profile server --function-id '<your-address>::channel::initialize'

Production Storage

For multi-instance deployments, swap the default in-memory stores for Redis:

import Redis from 'ioredis';
import { RedisStore } from 'aptosmpp/server';
import { RedisChannelStore } from 'aptosmpp';

const redis = new Redis(process.env.REDIS_URL);

MppxServer.create({ store: new RedisStore(redis), ... });
MppxSessionServer.create({ store: new RedisChannelStore(redis), ... });

Repo Structure

aptosmpp/
├── src/
│   ├── server/         # MppxServer, RedisStore
│   ├── client/         # MppxClient, MppxSessionClient
│   └── session/        # Voucher signing, ChannelStore, RedisChannelStore, authorizers
├── move/
│   └── aptos_channel/  # Move smart contract (escrow + payment channels)
├── demo/               # Express server + Node client demo
└── tests/              # Unit + integration tests

Testing

npm test                    # unit tests, no network needed
npm run test:integration    # runs against devnet, requires .env
npm run demo:server         # start demo server
npm run demo:client         # run demo client

Spec

Implements draft-httpauth-payment-00 and draft-payment-intent-charge-00.

Built on the MPP spec by Tempo + Stripe. This is an independent open-source implementation — not a Tempo product. Any Aptos wallet works as the paying client.

License

Apache-2.0