// skipContentSha256Cksum returns true if caller needs to skip
// payload checksum, false if not.
func skipContentSha256Cksum(r *http.Request) bool {
	var (
		v  []string
		ok bool
	)

	if isRequestPresignedSignatureV4(r) {
		v, ok = r.Form[xhttp.AmzContentSha256]
		if !ok {
			v, ok = r.Header[xhttp.AmzContentSha256]
		}
	} else {
		v, ok = r.Header[xhttp.AmzContentSha256]
	}

	// Skip if no header was set.