poloniex api query - lua

require 'crypto'
https = require 'ssl.https'

local key, secret = "89QK21JO-8O72SN4U-ZUR4CGE5-TSGNT63S",
                    "50c94254737f8a47364eb6825055fd93c5cf9b2e927d366e7acdf22e58e89e3fa2c32955d1feddc2f395a2d44507c36167be348dbd44b3eae6d1019d938994cd"
local poloniex_url = "https://poloniex.com/tradingApi"
local post_data = "nonce=" .. 1399116375497 .. "&command=returnBalances"--os.time()
local signature = crypto.hmac.digest("sha512", post_data, secret)
print(poloniex_url)
print("sha512:", signature)
https.request
{
  method = "POST",
  url = poloniex_url,
  headers = { Key = key, Sign = signature },
  source = ltn12.source.string(post_data),
  sink = ltn12.sink.file(io.stdout)
}