https://damienbod.com/2016/12/18/implementing-a-client-white-list-using-asp-net-core-middleware/
2020-03-09 Update .NET Core 3.1
2018-08-30 Added support for IP6
https://docs.microsoft.com/en-us/dotnet/framework/network-programming/ipv6-addressing
https://docs.microsoft.com/en-us/dotnet/framework/network-programming/internet-protocol-version-6
https://docs.microsoft.com/en-us/previous-versions/dotnet/netframework-3.0/ms180981(v=vs.85)