Refactor Cache-Control and Vary definitions (#24347)

spec/controllers/manifests_controller_spec.rb

@@ -7,11 +7,24 @@ describe ManifestsController do
 
   describe 'GET #show' do
     before do
-      get :show, format: :json
+      get :show
     end
 
     it 'returns http success' do
       expect(response).to have_http_status(200)
     end
+
+    it 'returns public cache control header' do
+      expect(response.headers['Cache-Control']).to include('public')
+    end
+
+    it 'does not set cookies' do
+      expect(response.cookies).to be_empty
+      expect(response.headers['Set-Cookies']).to be_nil
+    end
+
+    it 'does not set sessions' do
+      expect(session).to be_empty
+    end
   end
 end