code: func LoadClientCertificate(certFile string, keyFile string) (*tls.Certificate, error) {
  	if certFile != "" && keyFile != "" {
  		cert, err := tls.LoadX509KeyPair(certFile, keyFile)
  		if err != nil {
  			log.Critical("Unable to read client certificate from file: %s or key from file: %s", certFile, keyFile)
  			return nil, err
  		}
  		log.Debug("Client certificate loaded ")
  		return &cert, nil
  	}
  	return nil, nil
  }
docs: // LoadClientCertificate load key/certificate from pem files