config.exs

config :slackreceipt, :oauth
  consumer_key: "consumer-key",
  private_key_path: "/Users/joshdholtz/Projects/slackreceipt/priv/key.key"

xero.ex

defmodule Slackreceipt.Xero do
  @consumer {Application.get_env(:slackreceipt, :oauth)[:consumer_key], Application.get_env(:slackreceipt, :oauth)[:private_key_path], :rsa_sha1}

  def get(url, params) do
    :oauth.get(url, params, @consumer)
  end
end