Credentials for a proxy used when connecting to a https url do not seem to be used causing the url request to fail. Using proxy credentials with a http url works OK.
With a system wide proxy configured for both http and https on the Mac run the ProxyCredentialTests from the following repository:
The ProxyCredentialTests - NuGet3Api and HttpsAsyncRequestThroughProxy tests fail whilst the HttpAsyncThroughProxy one works with Mono 4.8.0.
With Mono 4.4.0 all three of these tests work.
The ProxyCredentialTests assume that Fiddler is being used as the proxy and the default username/password for Fiddler is hard coded at the top of the test.
Fixed in master and Mono 4.8
Looks good to me. Everything proxy related is now working in Xamarin Studio. Thanks.