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

System.Security.Cryptography.X509Certificates.X509ExtensionCollection

public int Count { get; }

public bool IsSynchronized { get; }

public X509Extension this[int index] { get; }

public X509Extension this[string oid] { get; }

public object SyncRoot { get; }

public int Add(X509Extension extension)

public void CopyTo(X509Extension[] array, int index)