func (c *missingSANChecker) CheckPeerCertificates(peerCertificates []*x509.Certificate) bool {
	if len(peerCertificates) > 0 {
		if serverCert := peerCertificates[0]; !hasSAN(serverCert) {
			return true
		}
	}

	return false
}

func hasSAN(c *x509.Certificate) bool {
	sanOID := []int{2, 5, 29, 17}

	for _, e := range c.Extensions {
		if e.Id.Equal(sanOID) {
			return true
		}
	}