map routes of an external service to use as phoenix routes

external_routes.ex

defmodule ExternalAPIRouter do
  use Phoenix.Router
  import Plug.Conn
  import Phoenix.Controller

  scope "/api/v1" do
    get("me2", __MODULE__, :me)
    get("product/:product_id", __MODULE__, :product_detail)
  end

  def build_conn() do
    Phoenix.ConnTest.build_conn()
    |> then(fn conn ->
      %Plug.Conn{conn | private: %{phoenix_router_url: "https://api.external.com"}}
    end)
  end
end

ExternalAPIRouter.build_conn()
|> ExternalAPIRouter.Helpers.external_api_router_url(:me)

ExternalAPIRouter.build_conn()
|> ExternalAPIRouter.Helpers.external_api_router_url(:me, [name: "Jorge"])

ExternalAPIRouter.build_conn()
|> ExternalAPIRouter.Helpers.external_api_router_url(:product_detail, "prdct12345")