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

System.Security.Cryptography.X509Certificates.X509Extension

public class X509Extension : AsnEncodedData
namespace System.Security.Cryptography.X509Certificates { public class X509Extension : AsnEncodedData { public bool Critical { get; set; } protected X509Extension(); public X509Extension(AsnEncodedData encodedExtension, bool critical); public X509Extension(Oid oid, byte[] rawData, bool critical); public X509Extension(string oid, byte[] rawData, bool critical); } }