Golang net / http包Post调用返回base64

Somehow below call returns base64 string instead of xml output. I need to decode this to see xml.

// POST 
func (u *UserResource) authenticateUser(request *restful.Request, response *restful.Response) {
    Api := new(Api)
    Api.url = "http://api.com"
    usr := new(User)
    err := request.ReadEntity(usr)
    if err != nil {
        response.AddHeader("Content-Type", "application/json")
        response.WriteErrorString(http.StatusInternalServerError, err.Error())
        return
    }

    buf := []byte("<api version=\"6.0\"><request>test</request></api>")

    r, err := http.Post(Api.url, "text/plain", bytes.NewBuffer(buf))
    if err != nil {
        response.AddHeader("Content-Type", "plain/text")
        response.WriteErrorString(http.StatusInternalServerError, err.Error())
        return
    }
    defer r.Body.Close()
    body, err := ioutil.ReadAll(r.Body)
    response.WriteHeader(http.StatusCreated)
    response.WriteEntity(body)
}

Is there a way to prevent this from happening and have correct xml output?