Hit App Sarahah Quietly Uploads Your Address Book

This might explain it a little better: https://www.charlesproxy.com/documentation/proxying/ssl-prox...

https://www.owasp.org/index.php/Certificate_and_Public_Key_P... Would be required

Even with HPKP, many libs/apps behave like Firefox/Chrome in this respect:

""" Firefox and Chrome disable pin validation for pinned hosts whose validated certificate chain terminates at a user-defined trust anchor (rather than a built-in trust anchor). This means that for users who imported custom root certificates all pinning violations are ignored.

"""

https://developer.mozilla.org/en-US/docs/Web/HTTP/Public_Key...

https://www.charlesproxy.com/documentation/proxying/ssl-prox...