Certificate pinning also known as Public Key Pinning “is a mechanism for sites to specify which certificate authorities have issued valid certs for that site, and for user-agents to reject TLS connections to those sites if the certificate is not issued by a known-good CA.”
Sites that use certificate pinning will typically not be loaded in your browser if you are proxying it through ZAP.
In Firefox you can change the about:config pref: ‘security.cert_pinning.enforcement_level’ to ‘0’ or ‘1’
The levels supported are:
- 0 Don't enforce any pins
- 1 Enforce pins when the chain is not from a local root
- 2 Always enforce pins
This article: https://www.imperialviolet.org/2011/05/04/pinning.html states that Chrome will allow user installed root CA certificates to override pins.
Advice and guidance for other browsers appreciated :)