if cc == nil {
		return nil, nil
	}
	var address string
	if cc.URL != nil {
		address = *cc.URL
	}
	var certPool *x509.CertPool
	if len(cc.CABundle) > 0 {
		certPool = x509.NewCertPool()
		certPool.AppendCertsFromPEM(cc.CABundle)
	} else {
		var err error
		certPool, err = x509.SystemCertPool()
		if err != nil {
			return nil, err
		}
	}
	tlsClientConfig := &tls.Config{RootCAs: certPool, MinVersion: tls.VersionTLS12}

pkg crypto/x509, func ParsePKIXPublicKey([]uint8) (interface{}, error)
pkg crypto/x509, method (*CertPool) AddCert(*Certificate)
pkg crypto/x509, method (*CertPool) AppendCertsFromPEM([]uint8) bool
pkg crypto/x509, method (*CertPool) Subjects() [][]uint8
pkg crypto/x509, method (*Certificate) CheckCRLSignature(*pkix.CertificateList) error