How can we use httpwebrequest in editor

I use AWSSDK for .net 3.5 to make custom editor to upload file to S3

And it keep throwing

 TlsException: Invalid certificate received from server. Error code: 0xffffffff800b010a

Which is relate to internal httpwebrequest

Even I have set

 ServicePointManager.ServerCertificateValidationCallback    = (obj,cert,chain,error) => true;

It then throwing ObjectDisposedException. And I can't read the response data