The point is that the key is never in the possession of the edge (i.e. Cloudflare). There is no way the edge could recover the key. They can use it to sign what

The point is that the key is never in the possession of the edge (i.e. Cloudflare). There is no way the edge could recover the key. They can use it to sign whatever they want, while you allow them to, although you can take whatever auditing measures you'd like there.