HPKP - Public Key Pinning

http://news.netcraft.com/archives/2016/03/22/secure-websites-shun-http-public-key-pinning.html

https://en.wikipedia.org/wiki/HTTP_Public_Key_Pinning

https://blog.qualys.com/ssllabs/2016/09/06/is-http-public-key-pinning-dead