Google announced plans to deprecate and eventually remove PKP support from the Chromium open-source browser. PKP, which stands for Public Key Pinning, is a system described in IETF RFC-7469 that webmasters can use with HTTPS sites. It allows a site operator to set an HTTP header for his site. When users connect to the website for the first time, the PKP header tells the user’s browser to download a list of public keys generated against the site’s HTTPS certificate. When the user comes back to the site again, the browser will take one of the keys and attempt to verify if it matches the site.
Source: https://www.bleepingcomputer.com/news/security/google-to-remove-public-key-pinning-pkp-support-in-chrome/