Discourse: CSRF-tokens on pages without no-cache headers, resulting in ATO when using CloudFlare proxy (Web Cache Deception)

Hi, I noticed this issue on one of your clients which was using CloudFlare in front of their Discourse. This is not affecting try.discourse.org but the same underlying issue can be seen there as well even though it's not exploitable on that specific domain. The TL;DR of issue is basically:...