MQTT Publisher sample console application to demonstrate connecting to AWS IoT

mqtt-publisher.cs

using System;
using System.Text;
using System.Security.Cryptography.X509Certificates;

using uPLibrary.Networking.M2Mqtt;

namespace MQTT.Sample
{

public class Program
    {
        /// <summary>
        /// AWS IoT endpoint - replace with your own
        /// </summary>
        private const string IotEndpoint = "*******.iot.eu-west-1.amazonaws.com";
        /// <summary>
        /// TLS1.2 port used by AWS IoT
        /// </summary>
        private const int BrokerPort = 8883;
        /// <summary>
        /// this must match - partially - what the subscribed is subscribed too
        /// nicksthings = the THING i created in AWS IoT
        /// t1/t555 is just an arbitary topic that i'm publishing to. (It needs 2 parts for the rule I'm using to work)
        /// </summary>
        private const string Topic = "YOURTHING/t1/t555";

        public static void Main(string[] args)
        {
            var publisher = new Program();
            publisher.Publish();
        }
        /// <summary>
        /// Configure client and publish a message
        /// </summary>
        public void Publish()
        {
            //convert to pfx using openssl - see confluence
            //you'll need to add these two files to the project and copy them to the output (not included in source control deliberately!)
            var clientCert = new X509Certificate2("YOURPFXFILE.pfx", "YOURPFXFILEPASSWORD");
            var caCert = X509Certificate.CreateFromSignedFile("root.pem");
            // create the client
            var client = new MqttClient(IotEndpoint, BrokerPort, true, caCert, clientCert, MqttSslProtocols.TLSv1_2);
            //message to publish - could be anything
            var message = "Insert your message here";
            //client naming has to be unique if there was more than one publisher
            client.Connect("clientid1");
            //publish to the topic
            client.Publish(Topic, Encoding.UTF8.GetBytes(message));
            //this was in for debug purposes but it's useful to see something in the console
            if (client.IsConnected)
            {
                Console.WriteLine("SUCCESS!");
            }
            //wait so that we can see the outcome
            Console.ReadLine();
        }

    }
    
}

I've got error "A call to SSPI failed" , have any idea?

I've testing on Xamarin OSX

What I observed is : we need to publish with QOS level 1 to receive puback.
client.Publish(topic, Encoding.UTF8.GetBytes(msg), MqttMsgBase.QOS_LEVEL_AT_LEAST_ONCE,false);