Hi @Marco37 ,

Yep, probably this is firewall issue. I've recreated your scenario and I can confirm that approach I've described above will work. So, I created Service Principal and I assigned him Feed Reader permisson. Then I obtained access token using client credential flow and I used that token in following way.

TOKEN = YOUR_TOKEN
ORGANIZATION = YOUR_ORGANIZATION
PROJECT = YOUR_PROJECT

%pip install azure.identity --index-url "https://{TOKEN}@{ORGANIZATION}.pkgs.visualstudio.com/{PROJECT}/_packaging/MyTestFeed/pypi/simple/"