While pushing this PR, the answer was that this was already working! But kind of unintuitive, but smart as it re-uses whatever docker setup you got (i.e. credentials helpers).

So to get this working you:

% docker login registry.science.ru.nl
Username: bla
Password:
...

And then use uc deploy -f .../compose.yml just like you did before. Now it should pull from the private repo and things “just work”.