Since the topic dependend FAQ is not open for discussion, i’ll just post this here. Maybe it could be added to the FAQ: Fatal: could not read Username for - FAQ - Drone
I found another way to get mentioned error with gitea. I had a user with administrative rights for a repo. The repo belonged to an organization, the user did not. Even tough the user had all the necessary right to clone and otherweise work on the repo, the runner could not access it. Adding the user to the organization solved the problem.