Expose more properties of the connection validator context in MQTTnet.Server. Migrate return code to reason code.

Source/MQTTnet.Server/Mqtt/MqttServerConnectionValidator.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Threading.Tasks;
+using IronPython.Runtime;
+using Microsoft.Extensions.Logging;
+using MQTTnet.Protocol;
+using MQTTnet.Server.Scripting;
+
+namespace MQTTnet.Server.Mqtt
+{
+    public class MqttServerConnectionValidator : IMqttServerConnectionValidator
+    {
+        private readonly PythonScriptHostService _pythonScriptHostService;
+        private readonly ILogger _logger;
+
+        public MqttServerConnectionValidator(PythonScriptHostService pythonScriptHostService, ILogger<MqttServerConnectionValidator> logger)
+        {
+            _pythonScriptHostService = pythonScriptHostService ?? throw new ArgumentNullException(nameof(pythonScriptHostService));
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        }
+
+        public Task ValidateConnectionAsync(MqttConnectionValidatorContext context)
+        {
+            try
+            {
+                var pythonContext = new PythonDictionary
+                {
+                    { "endpoint", context.Endpoint },
+                    { "is_secure_connection", context.IsSecureConnection },
+                    { "client_id", context.ClientId },
+                    { "username", context.Username },
+                    { "password", context.Password },
+                    { "raw_password", new Bytes(context.RawPassword) },
+                    { "clean_session", context.CleanSession},
+                    { "authentication_method", context.AuthenticationMethod},
+                    { "authentication_data", new Bytes(context.AuthenticationData)},
+
+                    { "result", PythonConvert.Pythonfy(context.ReasonCode) }
+                };
+
+                _pythonScriptHostService.InvokeOptionalFunction("on_validate_client_connection", pythonContext);
+
+                context.ReasonCode = PythonConvert.ParseEnum<MqttConnectReasonCode>((string)pythonContext["result"]);
+            }
+            catch (Exception exception)
+            {
+                _logger.LogError(exception, "Error while validating client connection.");
+            }
+
+            return Task.CompletedTask;
+        }
+    }
+}