It's not sufficient due to certificate pinning, and it also completely short-circuits any browser-based security policies keyed on the certificate or options ad

It's not sufficient due to certificate pinning, and it also completely short-circuits any browser-based security policies keyed on the certificate or options advertised in the protocol like SPDY. That would be the worst possible outcome, and why any correct solution (i.e doesn't break security or functionality) would be hard to reach