Simple feature to add.
Add a property to the ssl configuration for ValidateCRL or EnforceCRLValidation.
Use this property in the SSLStream. AuthenticateAsClientAsync call instead of FALSE as it is now.
Also, why call the async method with getawaiter().getresult() instead of just calling the synchronous version?.
GetResult() is really normally only called by the .NET library itself.
Its all a simple change and that will improve security.