The default behavior of most ACME clients is to generate a new key pair
at each renewal. While this choice is respectable and perfectly
justified in most configuration, it is also quite incompatible with the
use of HTTP Public Key Pinning (HPKP). Although HPKP is not wildly
supported and sometimes deprecated, users wishing to use it should not
be blocked.
https://tools.ietf.org/html/rfc7469https://en.wikipedia.org/wiki/HTTP_Public_Key_Pinning