When using Varnish, editing a Landing Page in Page Builder preview requires logging in for the first time. After that editor works as intended.

Requirements:
1. eZ Platform EE with Varnish

*Steps to reproduce:
1. Login as admin
2. Go to Page -> site
3. Choose "Edit"

Expected:
I'm in LP Edit mode

Actual:
I'm redirected to login page in Page Builder editor.