default_context.go
func (d *DefaultContext) LogFields(values map[string]interface{}) {
	d.logger = d.logger.WithFields(values)
}
func (d *DefaultContext) LogFields(values map[string]interface{}) {
	d.logger = d.logger.WithFields(values)
}
// LogFields adds the key/value pairs onto the Logger to be printed out
// as part of the request logging. This allows you to easily add things
// like metrics (think DB times) to your request.