I'm using a cloud service, you know, syncthemcalendars (https://syncthemcalendars.com), for to synchronize my calendars (Outlook and Google, very handy) for manage my availability without showin' my private appointments. The problem, it is to securing this flow! It send so much data to cloud servers on a regular basis. I would like to know how you guys manage this kind of permanent SaaS/cloud connection on the firewall. Is there a specific rule with Suricata or maybe Zenarmor, or some filtering trick, for to isolate this traffic without block it?
Most surely not. Either the cloud service supports encryptrion or it doesn't. You cannot encrypt on your side of the connection only.
On the other hand, if it is encrypted, you cannot decrypt it, because the client can verify the identity of the server (which it surely will) and not connect if a different certificate is presented.