<PackageReference Include="NETStandard.Library" Version="2.0.1" />

System.Net.Security.SslPolicyErrors

public enum SslPolicyErrors
namespace System.Net.Security { public enum SslPolicyErrors { None = 0, RemoteCertificateChainErrors = 4, RemoteCertificateNameMismatch = 2, RemoteCertificateNotAvailable = 1 } }