Make server certificate validation optional

source/implementations/f7/Meadow.F7/F7PlatformOS.cs

@@ -92,4 +92,52 @@ public int[] GetProcessorUtilization()
     {
         return new[] {100 - Core.Interop.Nuttx.meadow_idle_monitor_get_value()};
     }
+
+
+    /// <summary>
+    /// Enum representing different server certificate validation error returns.
+    /// </summary>
+    public enum ServerCertificateValidationError
+    {
+        InvalidMode = -1,
+        CannotChangeAfterInitialization = -2
+    }
+
+    /// <inheritdoc/>
+    public void SetServerCertificateValidationMode(ServerCertificateValidationMode authmode)
+    {
+        Resolver.Log.Trace($"Attempting to set the server certificate validation mode to {authmode}");
+
+        int authModeInt = (int)authmode;
+        if (authModeInt < 0 || authModeInt > Enum.GetNames(typeof(ServerCertificateValidationMode)).Length - 1)
+        {
+            string errorMessage = $"Invalid validation mode: {authModeInt}";
+            Resolver.Log.Error($"Invalid validation mode: {authModeInt}");
+            throw new ArgumentException(errorMessage);
+        }
+
+        int ret = Core.Interop.Nuttx.mono_mbedtls_set_server_cert_authmode(authModeInt);
+        if (ret == (int)ServerCertificateValidationError.InvalidMode)
+        {
+            string errorMessage = $"Invalid validation mode: {authModeInt}";
+            Resolver.Log.Error($"Invalid validation mode: {authModeInt}");
+            throw new ArgumentException(errorMessage);
+        }
+        else if (ret == (int)ServerCertificateValidationError.CannotChangeAfterInitialization)
+        {
+            string errorMessage = $"The server certificate validation mode cannot be changed after the TLS initialization.";
+            Resolver.Log.Error(errorMessage);
+            throw new Exception(errorMessage);
+        }
+        else if (ret < 0)
+        {
+            string errorMessage = $"Error setting validation mode.";
+            Resolver.Log.Error(errorMessage);
+            throw new Exception(errorMessage); 
+        }
+
+        Resolver.Log.Trace($"Server certificate validation mode set to {authmode} successfully!");
+
+        return;
+    }
 }

source/implementations/f7/Meadow.F7/Interop/Interop.cs

@@ -5,6 +5,7 @@ internal static partial class Interop
         public static partial class Nuttx
         {
             public const string LIBRARY_NAME = "nuttx";
+            public const string MBEDTLS_LIBRARY_NAME = "mbedtls";
         }
     }
 }

source/implementations/f7/Meadow.F7/Interop/Interop.mbedtls.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Runtime.InteropServices;
+namespace Meadow.Core;
+
+internal static partial class Interop
+{
+    public static partial class Nuttx
+    {
+        [DllImport(MBEDTLS_LIBRARY_NAME, SetLastError = true)]
+        public static extern int mono_mbedtls_set_server_cert_authmode(int authmode);
+    }
+}