使用FormData和身份验证在Go中发出POST请求

I'm currently trying to interface with an OAuth api with the example curl command curl -u {client_id}:{client_secret} -d grant_type=client_credentials https://us.battle.net/oauth/token. My current go file is:

package main

import (
    "bytes"
    "fmt"
    "mime/multipart"
    "net/http"
)

func checkErr(err error) bool {
    if err != nil {
        panic(err)
    }
    return true
}

func authcode(id string, secret string, cli http.Client) string {
    //un(trace("authcode"))
    var form bytes.Buffer
    w := multipart.NewWriter(&form)
    _, err := w.CreateFormField("grant_type=client_credentials")
    checkErr(err)
    req, err := http.NewRequest("POST", "https://us.battle.net/oauth/token", &form)
    checkErr(err)
    req.SetBasicAuth(id, secret)
    resp, err := cli.Do(req)
    checkErr(err)
    defer resp.Body.Close()
    json := make([]byte, 1024)
    _, err = resp.Body.Read(json)
    checkErr(err)
    return string(json)
}

func main() {
    //un(trace("main"))
    const apiID string = "user"
    const apiSecret string = "password"
    apiClient := &http.Client{}
    auth := authcode(apiID, apiSecret, *apiClient)
    fmt.Printf("%s", auth)
}

When I run this I get a response of {"error":"invalid_request","error_description":"Missing grant type"}

For reference, the api flow states:
"To request access tokens, an application must make a POST request with the following multipart form data to the token URI: grant_type=client_credentials

The application must pass basic HTTP auth credentials using the client_id as the user and client_secret as the password."
and the expected response is a json string containing an access token, token type, expiration in seconds, and the scope of functions available with said token

From curl manual we have:

       -d, --data <data>
          (HTTP)  Sends  the specified data in a POST request to the HTTP server, in the same way that a browser does when a user has filled in an HTML form and
          presses the submit button. This will cause curl to pass the data to the server using the content-type application/x-www-form-urlencoded.   Compare  to
          -F, --form.

Note the content-type application/x-www-form-urlencoded part.

as opposed to:

       -F, --form <name=content>
          (HTTP SMTP IMAP) For HTTP protocol family, this lets curl emulate a filled-in form in which a user has pressed the submit button. This causes curl  to
          POST data using the Content-Type multipart/form-data according to RFC 2388.

Therefore based on your curl, mime/multipart is probably not what you're looking for and you should be using Client.PostForm, from the manual of which we have:

The Content-Type header is set to application/x-www-form-urlencoded. To set other headers, use NewRequest and Client.Do.