If (like me) you’re working behind a proxy and thus cannot access the asset store from Unity3D’s editor (no way to configure any proxy),
here is a way to partially deal with it: simply access the asset store from your browser (which must have the proxy configuration set of course) !
Try this: https://kharma.unity3d.com (you will need your unity3d.com credentials)
“Partially” because you will only be able to browse the packages but not to download it 🙁
HTTPS access has been removed and I’ve no other solution 🙁
And by the way, as mentioned in the last unity3D blog post, a bunch of new assets have been added to the Art packages category, check it out!