How does Zero-Touch-Provisioning (ZTP) in Cisco SD-WAN work?

The Zero-Touch Provisioning (called ZTP) is the one of the concept behind SD-WAN that I mentioned here in What is SD-WAN article that I wrote about year ago. Frankly speaking, ZTP is something that every (or almost every) SD-WAN vendor has implemented. In this post I am going to dig into detail to the Cisco SDWAN ZTP.