Support TLS1.2 on .NET Framework 3.5

Program.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Net;
 using System.Windows.Forms;
 
 namespace TwitterClient
@@ -12,6 +13,7 @@ static class Program
         [STAThread]
         static int Main(string[] args)
         {
+            ServicePointManager.SecurityProtocol = SecurityProtocolTypeExtensions.Tls11 | SecurityProtocolTypeExtensions.Tls12;
             if (args.Length == 0) return 1;
             if (args[0] == "--config")
             {

SecurityProtocolTypeExtensions.cs

@@ -0,0 +1,10 @@
+namespace System.Net
+{
+    using System.Security.Authentication;
+    public static class SecurityProtocolTypeExtensions
+    {
+        public const SecurityProtocolType Tls12 = (SecurityProtocolType)SslProtocolsExtensions.Tls12;
+        public const SecurityProtocolType Tls11 = (SecurityProtocolType)SslProtocolsExtensions.Tls11;
+        public const SecurityProtocolType SystemDefault = (SecurityProtocolType)0;
+    }
+}

SslProtocolsExtensions.cs

@@ -0,0 +1,8 @@
+namespace System.Security.Authentication
+{
+    public static class SslProtocolsExtensions
+    {
+        public const SslProtocols Tls12 = (SslProtocols)0x00000C00;
+        public const SslProtocols Tls11 = (SslProtocols)0x00000300;
+    }
+}

TwitterClient.csproj

@@ -10,7 +10,7 @@
     <AppDesignerFolder>Properties</AppDesignerFolder>
     <RootNamespace>TwitterClient</RootNamespace>
     <AssemblyName>sstwitter</AssemblyName>
-    <TargetFrameworkVersion>v2.0</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v3.5</TargetFrameworkVersion>
     <FileAlignment>512</FileAlignment>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|x86' ">
@@ -51,6 +51,8 @@
     <Compile Include="OAuthBase.cs" />
     <Compile Include="Program.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="SecurityProtocolTypeExtensions.cs" />
+    <Compile Include="SslProtocolsExtensions.cs" />
     <Compile Include="Twitter.cs" />
     <Compile Include="TwitterToken.cs" />
     <Compile Include="WebClient.cs" />