This is only for secrets that are incredibly important to the point that their undetected loss could cause massive problems, I run these key ceremonies and I'm typing this from my bed on my work issued Macbook :)
I should have linked to an internal page that redirected there so people didn't get a misleading 404, but the internal coen repo is only open to all Monzo employees not the public because it contains some HSM specific stuff :( sorry - the public coen (which we're a fork of) is open though here https://github.com/iana-org/coen