code: func DefaultVerifyOptions() x509.VerifyOptions {
  	return x509.VerifyOptions{
  		KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
  	}
  }
docs: // DefaultVerifyOptions returns VerifyOptions that use the system root certificates, current time,
  // and requires certificates to be valid for client auth (x509.ExtKeyUsageClientAuth)