Add spec test for authComplete param carry-forward

spec/requests/application_controller_spec.rb

@@ -0,0 +1,17 @@
+require 'rails_helper'
+
+RSpec.describe ApplicationController do
+  describe '#redirect_to_login_if_required' do
+    let(:admin) { Fabricate(:admin) }
+
+    before do
+      admin  # to skip welcome wizard at home page `/`
+      SiteSetting.login_required = true
+    end
+
+    it "should carry-forward authComplete param to login page redirect" do
+      get "/?authComplete=true"
+      expect(response).to redirect_to('/login?authComplete=true')
+    end
+  end
+end