Problem

There is currently no native cross-platform, CI independent mechanism to test Certificate Authentication in Invoke-WebRequest and Invoke-RestMethod.

Proposal

Create a docker container to house a minimal aspnetcore app to validate Client Certificate presence in calls made by Invoke-WebRequest and Invoke-RestMethod. The docker container will need a self-signed certificate, SSL/TLS configuration, and be Linux based (debian jessie?). The aspnetcore app will need to, at minimum, echo whether a Client Certificate was presented or not and possibly include details about the Client Certificate. The entire solution will need to work in both AppVeyor and Travis CI and be as CI agnostic as possible.

see #4546