C# - .NET Framework 4.5.2 이하의 버전에서 HttpWebRequest로 https 호출 시 "System.Net.WebException" 예외 발생

아래의 코드를 .NET 4.5.2 이하의 버전에서 실행하면,

using System;

internal class Program
{
    static void Main(string[] args)
    {
        string target = "https://msdl.microsoft.com/download/symbols/ntdll.pdb/09f4753312350aebf684ab6e5dff76a61/ntdll.pdb";

        System.Net.HttpWebRequest req = System.Net.WebRequest.Create(target) as System.Net.HttpWebRequest;
        req.Method = "HEAD";

        using (System.Net.HttpWebResponse resp = req.GetResponse() as System.Net.HttpWebResponse)
        {
            Console.WriteLine(resp.ResponseUri);
        }
    }
}

Unhandled Exception: System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
   at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
   --- End of inner exception stack trace ---
   at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
   at System.Net.FixedSizeReader.ReadPacket(Byte[] buffer, Int32 offset, Int32 count)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest, Boolean renegotiation)
   at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
   at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
   at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size)
   at System.Net.ConnectStream.WriteHeaders(Boolean async)
   --- End of inner exception stack trace ---
   at System.Net.HttpWebRequest.GetResponse()
   at Program.Main(String[] args)

C# - WebClient로 https 호출 시 "The request was aborted: Could not create SSL/TLS secure channel" 예외 발생
; https://www.sysnet.pe.kr/2/0/13233

using System;

internal class Program
{
    static void Main(string[] args)
    {
        ServicePointManager.SecurityProtocol |= (SecurityProtocolType)3072;
        // 또는, 
        // ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls12;

        string target = "https://msdl.microsoft.com/download/symbols/ntdll.pdb/09f4753312350aebf684ab6e5dff76a61/ntdll.pdb";

        System.Net.HttpWebRequest req = System.Net.WebRequest.Create(target) as System.Net.HttpWebRequest;
        req.Method = "HEAD";

        using (System.Net.HttpWebResponse resp = req.GetResponse() as System.Net.HttpWebResponse)
        {
            Console.WriteLine(resp.ResponseUri);
        }
    }
}