mppx

TypeScript SDK for the "Payment" HTTP Authentication Scheme. Full 402 flow: challenge → credential → receipt.

What I can accomplish

• Add 402 payment handling to a client with Fetch.polyfill or Fetch.from.
• Protect HTTP routes with server-side MPP Challenges and Receipt responses.
• Accept one-time Tempo stablecoin payments with tempo.charge.
• Accept metered Tempo stablecoin payments with tempo.session.
• Accept one-time card payments with stripe.charge.
• Verify Credentials directly for custom transports or background workflows.
• Wrap MCP clients and servers so tool calls can require payment.

Required inputs

• Client integrations need a signing account and one or more client payment methods.
• Server integrations need a recipient, currency, amount, and MPP_SECRET_KEY.
• Tempo examples use chain ID 4217 unless a page explicitly covers Moderato testnet.
• Stripe examples need a configured Stripe account and Shared Payment Token flow.
• MCP integrations need the MCP client or server object to wrap.

Constraints

• Keep MPP_SECRET_KEY server-side and out of logs.
• Never commit private keys or wallet seeds.
• Treat runtime 402 Challenges as authoritative for current payment terms.
• Return id and opaque unchanged when responding to a Challenge.
• Use USDC.e for Tempo bridged USDC examples, not generic USDC.

Client

import { Mppx, tempo } from 'mppx/client'

// Polyfills globalThis.fetch to handle 402 automatically
Mppx.create({
  methods: [tempo({ account })],
})

const res = await fetch('https://api.example.com/resource')

Without polyfilling:

const mppx = Mppx.create({
  methods: [tempo({ account })],
  polyfill: false,
})

const res = await mppx.fetch('https://api.example.com/resource')

Server

import { Mppx, Store, tempo } from 'mppx/server'
import { privateKeyToAccount } from 'viem/accounts'

const account = privateKeyToAccount('0x...')