To check TLS version at .NET APP level

CheckSecurityProtocols.aspx

<%@ Page Language="C#" AutoEventWireup="true" %>
<%@ Import Namespace="Sitecore.Configuration" %>
<%@ Import Namespace="System.Web" %>
<%@ Import Namespace="System.Net" %>

<%
/*  https://stackoverflow.com/questions/28286086/default-securityprotocol-in-net-4-5 */
// print initial status
    Response.Write("Runtime: " + System.Diagnostics.FileVersionInfo.GetVersionInfo(typeof(int).Assembly.Location).ProductVersion);
    Response.Write("<br/>");
    Response.Write("Enabled protocols:   " + ServicePointManager.SecurityProtocol);
    Response.Write("<br/>");    
    Console.WriteLine("Available protocols: ");
    Boolean platformSupportsTls12 = false;
    foreach (SecurityProtocolType protocol in Enum.GetValues(typeof(SecurityProtocolType))) {                
        Response.Write(protocol.GetHashCode());
        if (protocol.GetHashCode() == 3072){
            platformSupportsTls12 = true;
        }
    }
    Response.Write("Is Tls12 enabled: " + ServicePointManager.SecurityProtocol.HasFlag((SecurityProtocolType)3072));    
    Response.Write("<br/>");

    /*
// enable Tls12, if possible

    if (!ServicePointManager.SecurityProtocol.HasFlag((SecurityProtocolType)3072)){
        if (platformSupportsTls12){
            Console.WriteLine("Platform supports Tls12, but it is not enabled. Enabling it now.");
            ServicePointManager.SecurityProtocol |= (SecurityProtocolType)3072;
        } else {
            Console.WriteLine("Platform does not supports Tls12.");
        }
    }

// disable ssl3
   if (ServicePointManager.SecurityProtocol.HasFlag(SecurityProtocolType.Ssl3)) { 
      Console.WriteLine("Ssl3SSL3 is enabled. Disabling it now.");
      // disable SSL3. Has no negative impact if SSL3 is already disabled. The enclosing "if" if just for illustration.
      System.Net.ServicePointManager.SecurityProtocol &= ~SecurityProtocolType.Ssl3;                      
   }
   */
   Response.Write("Enabled protocols:   " + ServicePointManager.SecurityProtocol);
%>