code: func LoadX509Signer(privateKeyPath, certPath string) (*X509Signer, error) {
  	pkey, err := ioutil.ReadFile(privateKeyPath)
  	if err != nil {
  		return nil, err
  	}
  	cert, err := ioutil.ReadFile(certPath)
  	if err != nil {
  		return nil, err
  	}
  	signer := &X509Signer{
  		PrivateKeyPEM:  pkey,
  		CertificatePEM: cert,
  	}
  	if err = signer.Validate(); err != nil {
  		return nil, err
  	}
  	return signer, nil
  }
docs: // LoadX509Signer parses and validates private key and certificate PEM files.
  //
  // Returns X509Signer that is ready for work.