Http(s) proxy on nix-darwin only working for root for all nix-commands, not as normal user

… so I set all proxy variables in the system-wide profile to my authenticating proxy, and installed nix and nix-darwin on an old mac (with HighSierra).

Now I can run things like nix-channel --update as root, but not as normal user, even though all env vars (NIX... and ..._PROXY for both root and the normal user) are the same.

In the proxy-logs there appears to be no indication that nix commands executed as normal user are actually trying to use the proxy, leaving me to suspect that my env vars have no effect as normal user (but they do as root).

Any ideas?