// GO code
package main

import  ( 
  "fmt"
  "encoding/hex"
  "encoding/base64"
  "crypto/hmac"
  "crypto/sha256"
)

func main() {
  datestring := "08 Apr 2015 21:37:33 GMT"
  appid := "d6468df6c1e8419fb5ec50f62be9a28b"
  appkey:= "15c7a6e1a5bd73500db29dffd0e19b6c6228b044c64348a6f5d6d470c54fc208"
  path  := "/xxxxxxxxxxxx/xxxxxxx/api/v1/users/xxxxx/factors"
  
  step1 := "GET\\n"+datestring+"\\n"+appid+"\\n"+path
  fmt.Printf("%s\n",step1)
  
  step4 := "ApplicationID:" + makeHmac( step1, appkey )
  fmt.Printf("%s\n",step4)
  
  step6 := "Basic :" + base64.StdEncoding.EncodeToString([]byte(step4))
  fmt.Printf("%s\n", step6)
}

func makeHmac(data string, key string) string {
  byteKey, _ := hex.DecodeString(key)   
  byteData := []byte(data)
  sig := hmac.New(sha256.New, byteKey)
  sig.Write([]byte(byteData))
  return base64.StdEncoding.EncodeToString(sig.Sum(nil))
}