You should use Soup.Session::authenticate: instead of building the Authorization header yourself.

Yeah, i know about Soup.Session::authenticate. The thing is that Jenkins only supports preemptive authentication which basically means that you get rejected right away (403 - forbidden) on the first request if you dont provide any authentication information. Using the authentication method of Soup would mean that Soup tries to request the URL, returns a SoupAuth object (which if have to provide with the username/password), then tries to request the URL again with the authentication information. I tried to do it this "soup-way" first but, like I already said, I get rejected right away on the first request. So I dont even get a SoupAuth object which I can then use to provide username and password. Thats why I chose to inject the authentication header myself. You want me to put in some more comments to clarify this circumstance? I'd also be delighted if you know another solution to this :-)

hey, its been one week :-( is somebody still reviewing this?