How I'd like to replace certificate pinning: * The client requests additional certificate chains * The server returns multiple certificate chains (typically t

How I'd like to replace certificate pinning: * The client requests additional certificate chains * The server returns multiple certificate chains (typically two), one chaining to a public CA, once chaining to a private CA * The connection only succeeds if all expected chains are present and valid * The public-key of the leaf certificates must be identical This means: * The public chain can follow standard practices around certificate transparency, renewal, revocation, expiration, etc. * Clients which don't care about pinning but expect a standard public chain will work * The chain to the private CA protects against a compromised public CA for clients which request/validate it * Requiring identical public-keys means that this only impacts chain validation, not the key-exchange