code: func PrivateKeyFromString(key []byte) (*rsa.PrivateKey, error) {
  	block, _ := pem.Decode(key)
  	if block == nil {
  		return nil, fmt.Errorf("private key block size invalid")
  	}
  	rsaKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
  	if err != nil {
  		return nil, err
  	}
  	return rsaKey, nil
  }
docs: // PrivateKeyFromString parses an RSA private key from a string