import (
    // ...
    "github.com/knadh/koanf/providers/kiln"
)

// Load encrypted environment variables with transformations
k.Load(kiln.Provider("kiln.toml", "", "production", kiln.Opt{
    Prefix: "API_",
    TransformFunc: func(k, v string) (string, any) {
        return strings.ToLower(strings.ReplaceAll(k, "_", ".")), v
    },
}), nil)