<PackageReference Include="NETStandard.Library" Version="2.0.0-preview2-25401-01" />

System.Net.AuthenticationSchemes

public enum AuthenticationSchemes
namespace System.Net { public enum AuthenticationSchemes { Anonymous = 32768, Basic = 8, Digest = 1, IntegratedWindowsAuthentication = 6, Negotiate = 2, None = 0, Ntlm = 4 } }