具有自定义标签的Golang Marshal / Unmarshal json

I want to Marshal / Unmarshal Golang object (json) with a custom tag.

Like

type Foo struct {
    Bar string `json:"test" es:"bar"`
}

data, _ := json.MarshalWithESTag(Foo{"Bar"})
log.Println(string(data)) // -> {"foo":"bar"}

In other words, I whan to use the encoding/json library with a different tag here: https://github.com/golang/go/blob/master/src/encoding/json/encode.go#L1033

Thanks :)