feat: implement custom PLug to forward headers using a Absinthe.Plug

lib/absinthe/compose.ex

@@ -5,12 +5,16 @@ defmodule Absinthe.Compose do
       definition: %{
         schema_node: %{__private__: private},
         name: name
-      }
+      },
+      context: context
     } = resolution
 
     compose = get_in(private, [:meta, :compose])
     compose_module = Keyword.fetch!(compose, :from)
-    opts = Keyword.get(compose, :opts, [])
+
+    opts =
+      Keyword.get(compose, :opts, [])
+      |> forward_hearders(context)
 
     {query, variables} = Absinthe.Compose.QueryGenerator.render(resolution)
 
@@ -24,4 +28,11 @@ defmodule Absinthe.Compose do
   def proxy(module, query, variables, opts, resolution) when is_atom(module) do
     apply(module, :resolve, [query, variables, opts, resolution])
   end
+
+  defp forward_hearders(opts, %{headers_to_forward: headers}) do
+    [headers: Keyword.get(opts, :headers, []) ++ headers]
+    |> Keyword.merge(opts)
+  end
+
+  defp forward_hearders(opts, _context), do: opts
 end

lib/absinthe/plug/forward_headers.ex

@@ -0,0 +1,28 @@
+defmodule Absinthe.Compose.Plug.ForwardHeader do
+  @moduledoc """
+  This Plug takes the given headers and add it to Absinthe.Plug context in order to be fowarded
+  on to the Upstream service on the resolver level.
+  """
+  @behaviour Plug
+
+  import Plug.Conn
+
+  def init(opts), do: opts
+
+  @spec call(Plug.Conn.t(), any) :: Plug.Conn.t()
+  def call(conn, opts) do
+    headers_to_forward = get_headers(conn, opts)
+    Absinthe.Plug.put_options(conn, context: %{headers_to_forward: headers_to_forward})
+  end
+
+  defp get_headers(conn, header_names) do
+    Enum.reduce(header_names, [], fn name, acc ->
+      name = String.downcase(name)
+
+      case get_req_header(conn, name) do
+        [] -> acc
+        values -> [{name, values} | acc]
+      end
+    end)
+  end
+end

mix.exs

@@ -45,7 +45,7 @@ defmodule AbsintheCompose.MixProject do
       """,
       links: %{
         github: "https://github.com/SpiffInc/absinthe_compose"
-      },
+      }
     ]
   end
 end

test/plug/forward_headers_test.exs

@@ -0,0 +1,36 @@
+defmodule Absinthe.Compose.Plug.ForwardHeaderTest do
+  use ExUnit.Case, async: true
+  use Plug.Test
+
+  alias Absinthe.Compose.Plug.ForwardHeader
+
+  setup do
+    ForwardHeader.init(["Auhtorization", "origin"])
+
+    conn =
+      conn("post", "/", "")
+      |> put_req_header("auhtorization", "some-token")
+      |> put_req_header("origin", "www.coolwebsite.com")
+      |> put_req_header("header-to-ignore", "ignored")
+
+    %{
+      conn: conn
+    }
+  end
+
+  test "fowards given headers to abshinte context", %{conn: conn} do
+    conn = ForwardHeader.call(conn, ["auhtorization", "Origin"])
+    assert %{context: %{headers_to_forward: headers_to_forward}} = conn.private[:absinthe]
+
+    assert [{"origin", ["www.coolwebsite.com"]}, {"auhtorization", ["some-token"]}] =
+             headers_to_forward
+
+    assert length(headers_to_forward) == 2
+  end
+
+  test "ignores non-existent headers", %{conn: conn} do
+    conn = ForwardHeader.call(conn, ["auhtorization", "origin", "some-giberish"])
+    assert %{context: %{headers_to_forward: headers_to_forward}} = conn.private[:absinthe]
+    assert length(headers_to_forward) == 2
+  end
+end