Cryptopia API from nodejs

client.js

const request = require('request')
const crypto = require('crypto')

const API_KEY = 'API KEY GOES HERE'
const API_SECRET = Buffer.from('SECRET GOES HERE', 'base64')

const md5 = str => crypto.createHash('md5').update(str).digest().toString('base64')
const hmac = str => crypto.createHmac('sha256', API_SECRET).update(str).digest().toString('base64')

const getBalance = (currency) => {
  const params = {Currency: currency}
  const url = 'https://www.cryptopia.co.nz/api/GetBalance'

  const nonce = ''+Date.now()
  const data = JSON.stringify(params)
  const digest = md5(data)

  // WHYYYY?
  const u2 = encodeURIComponent(url).toLowerCase()
  const sig = API_KEY + 'POST' + u2 + nonce + digest
  
  const signed = hmac(sig)
  const auth = 'amx ' + API_KEY + ':' + signed + ':' + nonce

  const headers = {
    'Authorization': auth,
    'Content-Type': 'application/json; charset=utf-8',
  }
  
  request.post({
    url,
    headers,
    body: data,
  }, (err, result) => {
    console.log(err, result && result.body)
  })
}

getBalance('BTC')