What causes this golang os.Exec behavior (escaped double quotes)?

I have the following code:

for i := 0; i < 1; i++ {
	wait := rand.Int63n(150) + 300
	time.Sleep(time.Millisecond * time.Duration(wait))
	//
	useragent := "--user-agent='Mozilla/5.0 (X11; CrOS armv7l 8872.76.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.105 Safari/537.36'"
	outDirectory := "--output-document=temp/review-" + strconv.Itoa(i) + ".html"
	header := "--header=\"Content-Type: application/x-www-form-urlencoded;charset=utf-8\""
	uri := "https://play.google.com/store/getreviews"
	payload := "--post-data=id=fi.danskebank.mobilepay&reviewSortOrder=2&xhr=1&reviewType=0&pageNum=" + strconv.Itoa(i)
	cmd := exec.Command("wget", useragent, outDirectory, header, uri, payload)
	fmt.Println(strings.Join(cmd.Args, " "))
	bytes, _ := cmd.CombinedOutput()
	fmt.Println(string(bytes))
}
fmt.Println("Finished crawling")

If I change the payload line from

payload := "--post-data=id=fi.danskebank.mobilepay&reviewSortOrder=2&xhr=1&reviewType=0&pageNum=" + strconv.Itoa(i)

to

payload := "--post-data=\"id=fi.danskebank.mobilepay&reviewSortOrder=2&xhr=1&reviewType=0&pageNum=" + strconv.Itoa(i) + "\""

It will return Server Error 500, even though when running the corresponding wget:

wget --user-agent='Mozilla/5.0 (X11; CrOS armv7l 8872.76.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.105 Safari/537.36' --output-document=temp/review-0.html --header="Content-Type: application/x-www-form-urlencoded;charset=utf-8" https://play.google.com/store/getreviews --post-data="id=fi.danskebank.mobilepay&reviewSortOrder=2&xhr=1&reviewType=0&pageNum=0"

It will have same response as the post-data without escaped quotes.

Why does Golang os.Exec result in this behavior?

When you execute the command in your shell, the shell processes the quotes and they aren't passed to the program you're executing. When you execute a command in Go, there is no shell processing involved, so the quotes are passed through. Since the program isn't expecting them, they get passed through directly in the request body, and the server responds with an error.

Unrelated to your issue, but if you don't have a specific reason to use wget, you'd get far better performance using the built-in HTTP client than forking out to wget for every request.