CA() (*tls.CA, error) {  key, cert, err := tls.ReadCACert("proxy-client-ca", lp.GeneratedCertsDirectory)  if err != nil {   return nil, fmt.Errorf("error reading proxy-client CA certificate/key: %v", err)  }  return &tls.CA{   Cert: cert,   Key:  key,  }, nil }  // Generate