Add UserFetcherPlug.

test/plugs/user_fetcher_plug_test.exs

@@ -0,0 +1,37 @@
+defmodule Pleroma.Plugs.UserFetcherPlugTest do
+  use Pleroma.Web.ConnCase, async: true
+
+  alias Pleroma.Plugs.UserFetcherPlug
+  import Pleroma.Factory
+
+  setup do
+    user = insert(:user)
+    %{user: user}
+  end
+
+  test "if an auth_credentials assign is present, it tries to fetch the user and assigns it", %{
+    conn: conn,
+    user: user
+  } do
+    conn =
+      conn
+      |> assign(:auth_credentials, %{
+        username: user.nickname,
+        password: nil
+      })
+
+    conn =
+      conn
+      |> UserFetcherPlug.call(%{})
+
+    assert conn.assigns[:auth_user] == user
+  end
+
+  test "without a credential assign it doesn't do anything", %{conn: conn} do
+    ret_conn =
+      conn
+      |> UserFetcherPlug.call(%{})
+
+    assert conn == ret_conn
+  end
+end