hi again.
In the attempt to share some thoughts and possibly find a solution, I have uploaded the simplest PB.NET test case at
https://www.dropbox.com/s/z7xfpab52nv20gs/restful.zip?dl=0
(set your github user/pwd in the proxy object's constructor).
My test server is https://api.github.com/user, so "direct authentication" or "challenge/response" configurations are not an issue here: authentication against Github simply works from Fiddler4 but it does not from PB.
This picture
https://www.dropbox.com/s/p5neoyi4y5z9hw6/fiddler.png?dl=0
shows that when the RESTful service is called from Fiddler4 the HTTP header contains basic authentication info, whereas the same request from PB does not.
Any help is truly appreciated.
Best,
Marco