Fixes #140 ... failed to create safe SSL/TLS context

Wizard/PackageInfo.cs

@@ -28,6 +28,7 @@
 using System.Net;
 using System.Text.RegularExpressions;
 using System.Threading.Tasks;
+using net.r_eg.MvsSln.Extensions;
 using net.r_eg.MvsSln.Log;
 
 namespace net.r_eg.DllExport.Wizard
@@ -53,6 +54,8 @@ public PackageInfo(IExecutor exec)
         {
             this.exec   = exec ?? throw new ArgumentNullException(nameof(exec));
             proxy       = exec.Config.Proxy?.Trim();
+
+            DefineSecurityProtocol();
         }
 
         /// <summary>
@@ -145,5 +148,19 @@ private WebProxy GetProxy(string cfg)
                 )
             };
         }
+
+        private static void DefineSecurityProtocol()
+        {
+            // https://github.com/3F/DllExport/issues/140
+            // Since Tls13 (0x3000) is not available from obsolete assemblies,
+            //    and SecurityProtocolType.SystemDefault (0) is defined only for netfx 4.7+, 4.8;
+            //    We can try to bind this at runtime using the last available environment where this code was executed.
+
+            // NOTE: ServicePointManager.SecurityProtocol = 0 may produce the following problem: An unexpected error occurred on a receive.
+
+            Enum.GetValues(typeof(SecurityProtocolType))
+                .Cast<SecurityProtocolType>()
+                .ForEach(s => ServicePointManager.SecurityProtocol |= s);
+        }
     }
 }