Certificate is not included in the webhook request

Hi, we are trying to implement a full API workflow, including webhooks. As of now, we are succesfully handling the webhook. As a next step, we'd like to add authentication to that. I've added a test certificate to the account and I was trying to handle that in our C# code. I am not currently able to access it with "HttpContext.Connection.ClientCertificate".  Could this be an issue with the certificate or with how we are trying to handle things? There doesn't seem to be much support for webhook authentication in the documentation.

Thanks