Fetch.polyfill

Choose a signing account

import { privateKeyToAccount } from 'viem/accounts'

export const account = privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`)

Replaces globalThis.fetch with a payment-aware wrapper that handles 402 Payment Required responses.

Payment retries use redirect: 'manual' to keep Credentials from following redirects. A 3xx response returns to you and leaves payment acceptance pending. The initial request retains its configured redirect behavior.

Usage

import { Provider } from 'accounts'
import { Fetch, tempo } from 'mppx/client'
 
const provider = Provider.create({ mpp: false }) // Avoid double 402 handling; mppx is configured below.
await provider.request({ method: 'wallet_connect' })
 
Fetch.polyfill({
  methods: [tempo({
    account: provider.getAccount({ signable: true }),
    getClient: provider.getClient,
  })],
})
 
const response = await fetch('https://mpp.dev/api/ping/paid')
console.log(response.status)
200

import { Fetch, tempo } from 'mppx/client'
import { privateKeyToAccount } from 'viem/accounts'
 
const account = privateKeyToAccount('0x...')
 
Fetch.polyfill({
  methods: [tempo({ account })],
})
 
const response = await fetch('https://mpp.dev/api/ping/paid')
console.log(response.status)
200

With cross-origin payments

In browsers, Fetch.polyfill defaults to same-origin Accept-Payment injection. Pass acceptPaymentPolicy when your paid API lives on another origin.

import { Provider } from 'accounts'
import { Fetch, tempo } from 'mppx/client'
 
const provider = Provider.create({ mpp: false }) // Avoid double 402 handling; mppx is configured below.
await provider.request({ method: 'wallet_connect' })
 
Fetch.polyfill({
  acceptPaymentPolicy: {
    origins: ['https://api.example.com'],
  },
  methods: [tempo({
    account: provider.getAccount({ signable: true }),
    getClient: provider.getClient,
  })],
})

import { Fetch, tempo } from 'mppx/client'
import { privateKeyToAccount } from 'viem/accounts'
 
const account = privateKeyToAccount('0x...')
 
Fetch.polyfill({
  acceptPaymentPolicy: {
    origins: ['https://api.example.com'],
  },
  methods: [tempo({ account })],
})

Return type

type ReturnType = void

Parameters

acceptPayment (optional)

• Type: AcceptPayment.Resolved<methods>

Resolved Accept-Payment header and preference data.

acceptPaymentPolicy (optional)

• Type: 'always' | 'same-origin' | 'never' | { origins: readonly string[] }
• Default: 'same-origin' in browsers, 'always' otherwise

Controls when Accept-Payment is injected.

eventDispatcher (optional)

• Type: ClientEventDispatcher<methods>

Advanced shared event dispatcher. challenge.received handlers run before onChallenge; the first non-empty Credential string skips onChallenge.

fetch (optional)

• Type: typeof globalThis.fetch
• Default: globalThis.fetch

Custom fetch function to wrap.

methods

• Type: readonly Method.AnyClient[]

Array of payment methods to use for 402 responses.

onChallenge (optional)

• Type: (challenge, helpers) => Promise<string | undefined>

Called after a 402 Challenge is selected and before the wrapper retries the request.

orderChallenges (optional)

• Type: (challenges: readonly Challenge[]) => readonly Challenge[]

Filters or reorders supported Challenges before Credential creation.

transport (optional)

• Type: Transport.AnyTransport
• Default: Transport.http()

Transport used to extract Challenges and attach Credentials.