Include measurements in HTTP header to forward them to clients for verifying

[ameba23]

This is a feature of cvm-reverse-proxy:

func (p *Proxy) copyMeasurementsToHeader(conn *tls.ConnectionState, header *http.Header) (int, error) {
	certs := conn.PeerCertificates
	atlsVariant, extractedMeasurements, err := GetMeasurementsFromTLS(certs, p.validatorOIDs)
	if err != nil {
		return http.StatusTeapot, err
	} else if extractedMeasurements == nil {
		p.log.Debug("[proxy-request: add-headers] no measurements, not adding headers")
		return 0, nil
	}

	measurementsInHeaderFormat := make(map[uint32]string, len(extractedMeasurements))
	for pcr, value := range extractedMeasurements {
		measurementsInHeaderFormat[pcr] = hex.EncodeToString(value)
	}

	marshaledPcrs, err := json.Marshal(measurementsInHeaderFormat)
	if err != nil {
		return http.StatusInternalServerError, errors.New("could not marshal measurement extracted from tls extension")
	}

	header.Set(AttestationTypeHeader, atlsVariant.String())
	header.Set(MeasurementHeader, string(marshaledPcrs))

	p.log.With(AttestationTypeHeader, atlsVariant.String()).With(MeasurementHeader, string(marshaledPcrs)).Debug("[proxy-request: add-headers] measurement headers added")
	return 0, nil
}

This is not so simple to add here as this is a generic TCP proxy service which doesn't (currently) assume HTTP or modify or parse traffic (besides the initial attestation).

[ameba23]

I actually think this is a bad pattern - attestation validation logic should happen where the TLS session terminates, not sent in the clear to another service (even if that connection is VM-internal).

That is, the services which check the measurements should ideally do the remote-attested TLS part themselves.

But im willing to go with this for now, in order to be able to integrate quickly.