Set encryption password for booting on OnePlus 5? How do you set a custom encryption password on the OnePlus 5 and make the system prompt for the password on boot?

The OnePlus One made this easy, but I can't figure out how to do it on the OnePlus 5.

(Otherwise what is the point of encryption if the device automatically decrypts itself?!?!)
I was trying to do this too, but it seems like this is by design as seen at  oneplus forum.

Apparently nothing gets decrypted after boot until you enter your pin/pattern but it's still a bit disappointing if you want the phone to not even boot without authentication.