Coinbase Pro REST API example in Elixir

coinbase_pro.ex

defmodule CoinbasePro do
  @moduledoc """
  CoinbasePro exchange wrapper.
  """

  @config Application.get_env(:config, __MODULE__)
  @api_url (if Mix.env == :prod do
    "https://api.pro.coinbase.com"
  else
    "https://api-public.sandbox.pro.coinbase.com"
  end)
  def api_url, do: @api_url

  @req_headers [
    {:"Content-Type", "application/json"},
    {:Accept, "application/json"}
  ]

  def place_order(payload) do
    path = "/orders"
    method = "POST"
    url = "#{@api_url}#{path}"
    ts = timestamp_str()

    body = Jason.encode!(payload)
    signature = build_signature(ts, path, method, body)
    headers = Keyword.merge(auth_headers(signature, ts), @req_headers)

    HTTPoison.request!(method, url, body, headers)
  end

  defp build_signature(timestamp, path, method, body) do
    message = "#{timestamp}#{method}#{path}#{body}"
    {:ok, decoded_secret} = Base.decode64(@config[:secret])
    Base.encode64(:crypto.hmac(:sha256, decoded_secret, message))
  end

  defp auth_headers(signature, access_timestamp) do
    [
      {:"CB-ACCESS-KEY", @config[:access_key]},
      {:"CB-ACCESS-SIGN", signature},
      {:"CB-ACCESS-TIMESTAMP", access_timestamp},
      {:"CB-ACCESS-PASSPHRASE", @config[:passphrase]}
    ]
  end

  defp timestamp_str do
    Integer.to_string(:os.system_time(:seconds))
  end
end