var handler = null;
try
{
    var cert = new X509Certificate2(OCEAN_CONNECT_SELFCERTPATH, OCEAN_CONNECT_SELFCERTPWD);
    handler = new WebRequestHandler();
    handler.ClientCertificates.Add(cert);

    var client = new HttpClient(handler);

    System.Net.ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(ValidarCertificado);
    System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;

    var values = new Dictionary<string, string>
    {
        { "appId", LITERAL_APPID },
        { "secret",LITERAL_SECRET }
    };

    var content = new FormUrlEncodedContent(values);

    var response = await client.PostAsync( URL, content);

    var responseString = await response.Content.ReadAsStringAsync();

    json = JObject.Parse(responseString);
}
catch(Exception ex)
{
    ...
}