GO Lang中的HTTP POST引发错误

I am trying to make a Post request using in GO Lang. The API URL is expecting a username and password field to be passed to it in body. However I keep getting the below error ?

I am not sure what am i doing wrong here ?

Error

 url.Values undefined (type string has no field or method Values)

Go Function

func makeHttpPostReq(url string, username string, password string){

    client := http.Client{}
    req, err := http.NewRequest("POST", url, url.Values{"username": {username}, "password": {password}})
    req.Header.Add("Content-Type", "application/x-www-form-urlencoded")

    resp, err := client.Do(req)
    if err != nil {
         fmt.Println("Unable to reach the server.")
    } else {
         body, _ := ioutil.ReadAll(resp.Body)
         fmt.Println("body=", string(body))
    }

}

The argument to makeHttpPostReq states url is a string but you are treating it as a struct url.Values, thus the error

has no field or method

You are reusing the url word.

url is in your case resolving to url as a string not a net/url