Payfast API: Easy Nodejs signature and headers function

Lets be real, Payfast API is confusing and their documentation is too.

If you want a nice reusable function that creates the signature and request headers for you please use this.

This will help you get less "Merchant authorization failed." and data discrepancy errors.

import crypto from "crypto"

function createPayfastHeaders(data) {
  // remember live and sandbox merchant_id and passphrase are different
  const merchant_id = "your_merchant_id"
  const passphrase = "your_pass_phrase"

  data = {
    ...data,
    passphrase,
  }

  const headers = {
    "merchant-id": merchant_id,
    "version": "v1",
    "timestamp": (new Date()).toISOString().split('.')[0],
    "signature": ""
  }

  const req_headers = new Headers()
  Object.keys(headers).forEach(key => {
    req_headers.append(key, headers[key])
  })

  const signature_data = {...data, ...headers}
  let signature_uri = "";
  Object.keys(signature_data).sort().forEach(key => {
    if (key !== "signature") {
      signature_uri += `${key}=${encodeURIComponent(signature_data[key]).replace(/%20/g, '+')}&`
    }
  });

  // Remove the last '&'
  signature_uri = signature_uri.substring(0, signature_uri.length - 1);

  const signature = crypto.createHash("md5").update(signature_uri).digest("hex");
  req_headers.set("signature", signature)
  req_headers.append("Content-Type", "application/json") // <- important

  return req_headers
}

Example on how to use it:

async function createRefund(payment_id, refund_params) {
  const headers = createPayfastHeaders(refund_params)

  const url = `https://api.payfast.co.za/refunds/${payment_id}?testing=true`; // <- add testing true for sandbox testing
  const response = await fetch(url, {
    method: "POST",
    headers: headers,
    body: JSON.stringify(refund_params)
  });

  return await response.json();
}

const refund = await createRefund("2120314", {
  amount: 1000,
  reason: "stock",
  notify_buyer: 0
});

Documentation:
https://developers.payfast.co.za/api#refund-create