verifyPeerCertificateCallback := func(called *bool, rawCerts [][]byte, validatedChains [][]*x509.Certificate) error {
		if l := len(rawCerts); l != 1 {
			return fmt.Errorf("got len(rawCerts) = %d, wanted 1", l)
		}
		if len(validatedChains) == 0 {
			return errors.New("got len(validatedChains) = 0, wanted non-zero")
		}
		*called = true
		return nil
	}