If you are on a server where you cannot install the newer .NET versions, then you may be restricted to ASP.NET 4.5. This does support TLS 1.2, but it is not used by default. You can force this by adding this code within the Application_Start event in the Global.asax file in the root of the web:
Try
System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12
Catch
End Try
