Authentication not working (always forbidden)

I'm trying to push a package using Nuget 3.4.3 and I'm getting Forbidden error whenever I try to push a package. I've tried username:password as the API key, and also entering it when prompted by Nuget. Nothing seems to work. Any ideas? I'm using Proget 4.0.13.

Product: ProGet
Version: 4.0.13

All of the things you described should work, and are used by a lot of other users. So, I would try to make sure you have the appropriate privileges on the feed, etc. Also make sure there's no intermediate proxies, etc.

Fiddler may help debug/diagnose.

Ok, I checked things with Fiddler, and the error that comes back is HTTP/1.1 403 There was an error processing the request: You are not authorized to add a package to this feed because the user builder does not have the Feeds_AddPackage privilege.

However, the user builder is a member of the Publishers group, which is associated with the Publish Packages task, globally scoped. If I'm not mistaken, this should be enough for the user to publish (and I don't see any other security settings anyway).

Any idea how to resolve this?

Hard to say exactly. The set-up you describe is very typical, and generally works fine...

I would make sure the credentials are being passed; you can test different combinations of things, such as giving anonymous user access, different privleges, etc.

I fixed it by uninstalling proget and nuking everything. I hope this isn't typical; I installed the latest version a year ago but never got to using it really, only created a few feeds and set permissions, and then recently updated to 4.0.13.

It was most certainly permissions related. From the 4.0 Upgrade Notes...

If you modified any of the default roles but did not rename then, then they will renamed to the new task names. In addition, the role's individually-securable actions (formerly, "tasks") will be reset to the new, default definitions