Agenix cli error in pure evaluation mode

[SamueleFacenda]

I've recently enabled pure evaluation mode in nix.conf. Now when I try to run agenix -e mysecret.age I get an error that states that access to absolute path '/nixos-config/secrets/secrets.nix' is forbidden in pure eval mode (use '--impure' to override) and I cannot proceed.
I don't know if this is intended (keeping the evaluation pure), but the fix would be to add the --impure flag to nix-instantiate in agenix.sh.
Personally I think that this would not have drawbacks, reading from a file is an impure operation and thus should be marked as such.