functions to extract SSL certs for Erlang SSL from ENV variables

ssl_cert_extraction_example.ex

  def ssl_config do
    ssl_config(client_cert, client_cert_key)
  end

  def ssl_config(_client_cert=nil, _client_cert_key=nil) do
    []
  end

  def ssl_config(client_cert, client_cert_key) do
    [
      ssl: [
        cert: client_cert,
        key: client_cert_key,
      ]
    ]
  end

  def client_cert do
    case System.get_env("CLIENT_CERT") do
      nil -> nil
      cert -> extract_der(cert)
    end
  end

  def client_cert_key do
    case System.get_env("CLIENT_CERT_KEY") do
      nil -> nil
      cert_key -> extract_type_and_der(cert_key)
    end
  end

  def decode_pem(pem) do
    pem
    |> :public_key.pem_decode
    |> List.first
  end

  def extract_der(cert) do
    {_type, der, _} = decode_pem(cert)
    der
  end

  def extract_type_and_der(cert_key) do
    {type, der_cert, _} = decode_pem(cert_key)
    {type, der_cert}
  end