resource.ex

defmodule MyApp.UserResource do
  use Phoenix.Resource
  
  defp get_user(%{"id" => id}) do
    Repo.get(User, id)
  end
  
  def supported_formats do
    ["html", "json", "xml"]
  end
  
  def authorized?(conn, params) do
    true
  end
  
  def handle_ok("json", conn, params) do
    user = get_user(params)
    %{
      name: user.name,
      email: user.email
    }
  end
  def handle_ok("xml", conn, params) do
    XMLBuilder.build(get_user params)
  end
  def handle_ok("html", conn, params) do
    render conn, "show.html", %{user: get_user(params)}
  end
end

There's a basic implementation of this port at https://github.com/sysdea-libs/wrangle now