Assign :user whenever :user_id is in session, pass to OAuth form

lib/pleroma/plugs/ensure_user_key_plug.ex

@@ -3,6 +3,7 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.Plugs.EnsureUserKeyPlug do
+  alias Pleroma.User
   import Plug.Conn
 
   def init(opts) do
@@ -12,7 +13,12 @@ defmodule Pleroma.Plugs.EnsureUserKeyPlug do
   def call(%{assigns: %{user: _}} = conn, _), do: conn
 
   def call(conn, _) do
-    conn
+    with user_id <- get_session(conn, :user_id),
-    |> assign(:user, nil)
+         true <- is_binary(user_id),
+         %User{} = user <- User.get_by_id(user_id) do
+      assign(conn, :user, user)
+    else
+      _ -> assign(conn, :user, nil)
+    end
   end
 end

lib/pleroma/web/router.ex

@@ -276,7 +276,7 @@ defmodule Pleroma.Web.Router do
 
   scope "/oauth", Pleroma.Web.OAuth do
     scope [] do
-      pipe_through(:oauth)
+      pipe_through([:oauth, :after_auth])
       get("/authorize", OAuthController, :authorize)
     end
 

test/plugs/ensure_user_key_plug_test.exs

@@ -4,8 +4,23 @@
 
 defmodule Pleroma.Plugs.EnsureUserKeyPlugTest do
   use Pleroma.Web.ConnCase, async: true
-
   alias Pleroma.Plugs.EnsureUserKeyPlug
+  import Pleroma.Factory
+
+  @session_opts [
+    store: :cookie,
+    key: "_test",
+    signing_salt: "cooldude"
+  ]
+
+  setup %{conn: conn} do
+    conn =
+      conn
+      |> Plug.Session.call(Plug.Session.init(@session_opts))
+      |> fetch_session()
+
+    %{conn: conn}
+  end
 
   test "if the conn has a user key set, it does nothing", %{conn: conn} do
     conn =
@@ -19,6 +34,17 @@ defmodule Pleroma.Plugs.EnsureUserKeyPlugTest do
     assert conn == ret_conn
   end
 
+  test "if the session has a user_id, it sets the user", %{conn: conn} do
+    user = insert(:user)
+
+    conn =
+      conn
+      |> put_session(:user_id, user.id)
+      |> EnsureUserKeyPlug.call(%{})
+
+    assert conn.assigns[:user] == user
+  end
+
   test "if the conn has no key set, it sets it to nil", %{conn: conn} do
     conn =
       conn