code: func KeyPair(domain string, expiration time.Time) ([]byte, []byte, error) {
  	rsaPrivKey, err := rsa.GenerateKey(rand.Reader, 2048)
  	if err != nil {
  		return nil, nil, err
  	}
  	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(rsaPrivKey)})
  
  	certPEM, err := PemCert(rsaPrivKey, domain, expiration)
  	if err != nil {
  		return nil, nil, err
  	}
  	return certPEM, keyPEM, nil
  }
docs: // KeyPair generates cert and key files