snippet3.go

...
func matchSignature(signature, key, payload string) bool {
	mac := hmac.New(sha1.New, []byte(key))
	mac.Write([]byte(payload))
	expectedHMAC := mac.Sum(nil)

	//signature format is sha1=foobarred
	githubHMAC, _ := hex.DecodeString(strings.Split(signature, "=")[1])
	match := hmac.Equal(githubHMAC, expectedHMAC)
	return match
}
...