func (c *Configuration) Set(path string, value interface{}, parser ...koanf.Parser) error {
	var p koanf.Parser
	if len(parser) > 0 {
		p = parser[0]
	}
	return c.config.Load(confmap.Provider(map[string]interface{}{
		strings.ToLower(path): value,
	}, "."), p)
}
Set sets the value for the key (case-insensitive).
package configuration
import (
	"strings"
	"github.com/knadh/koanf"
	"github.com/knadh/koanf/providers/confmap"
	"github.com/knadh/koanf/providers/structs"
)
func (c *Configuration) SetDefault(path string, value interface{}, parser ...koanf.Parser) error {
	if c.config.Exists(strings.ToLower(path)) {
		return nil
	}
	return c.Set(path, value, parser...)
}
func (c *Configuration) SetDefaultStruct(path string, value interface{}, fieldTag string, parser ...koanf.Parser) error {
	if c.config.Exists(strings.ToLower(path)) {
		return nil
	}
	return c.SetStruct(path, value, fieldTag, parser...)
}