Hm, do you have a better (and if possibly simpler) idea of solving this?

But I actually could change the [default value](https://github.com/aszlig/nixos/blob/ebb2c53741cae02afd6fa3d7b4ec017f1479ae45/modules/services/databases/postgresql.nix#L96-L97) to include peer connections for all accounts.

Although, it would bear the problem that it depends on the specified [package](https://github.com/aszlig/nixos/blob/ebb2c53741cae02afd6fa3d7b4ec017f1479ae45/modules/services/databases/postgresql.nix#L96-L97), eventually rendering it into a circular dependency.