Flake inputs' URLs igrnore credendtials from netrc?

I have /etc/nix/netrc file to specify credentials for an internal binary cache/substituter and also use the netrc-file option in net.conf which points to the same file. The nix builds are happy with this setup but it if I use the internal location in flakes inputs’ urls I get authentication errors, so it looks like the netrc settings are ignored in that case. Is there any way to make flakes use the netrc credentials?