[#1427] Reworked admin scopes support.

Requalified users.is_admin flag as legacy accessor to admin actions in case token lacks admin scope(s).

lib/pleroma/plugs/user_is_admin_plug.ex

@@ -5,19 +5,39 @@
 defmodule Pleroma.Plugs.UserIsAdminPlug do
   import Pleroma.Web.TranslationHelpers
   import Plug.Conn
+
   alias Pleroma.User
+  alias Pleroma.Web.OAuth
 
   def init(options) do
     options
   end
 
-  def call(%{assigns: %{user: %User{is_admin: true}}} = conn, _) do
-    conn
+  def call(%Plug.Conn{assigns: %{token: %OAuth.Token{scopes: oauth_scopes} = _token}} = conn, _) do
+    if OAuth.Scopes.contains_admin_scopes?(oauth_scopes) do
+      # Note: checking for _any_ admin scope presence, not necessarily fitting requested action.
+      #   Thus, controller must explicitly invoke OAuthScopesPlug to verify scope requirements.
+      conn
+    else
+      fail(conn)
+    end
+  end
+
+  unless Pleroma.Config.enforce_oauth_admin_scope_usage?() do
+    # To do: once AdminFE makes use of "admin" scope, disable the following func definition
+    #   (fail on no admin scope(s) in token even if `is_admin` is true)
+    def call(%Plug.Conn{assigns: %{user: %User{is_admin: true}}} = conn, _) do
+      conn
+    end
   end
 
   def call(conn, _) do
+    fail(conn)
+  end
+
+  defp fail(conn) do
     conn
-    |> render_error(:forbidden, "User is not admin.")
-    |> halt
+    |> render_error(:forbidden, "User is not an admin or OAuth admin scope is not granted.")
+    |> halt()
   end
 end