From 5931756ce5cec60c3213876980aa6038b6175b46 Mon Sep 17 00:00:00 2001
From: Pierre Carrier <pierre@gcarrier.fr>
Date: Wed, 24 Apr 2013 01:32:34 +0200
Subject: [PATCH] initial release

---
 .godir                 |  1 +
 Procfile               |  1 +
 googleauthenticator.go | 65 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 67 insertions(+)
 create mode 100644 .godir
 create mode 100644 Procfile
 create mode 100644 googleauthenticator.go

diff --git a/.godir b/.godir
new file mode 100644
index 0000000..61552c1
--- /dev/null
+++ b/.godir
@@ -0,0 +1 @@
+googleauthenticator
diff --git a/Procfile b/Procfile
new file mode 100644
index 0000000..0833915
--- /dev/null
+++ b/Procfile
@@ -0,0 +1 @@
+web: googleauthenticator
diff --git a/googleauthenticator.go b/googleauthenticator.go
new file mode 100644
index 0000000..bb59dd0
--- /dev/null
+++ b/googleauthenticator.go
@@ -0,0 +1,65 @@
+package main
+
+import (
+	"crypto/hmac"
+	"crypto/sha1"
+	"encoding/base32"
+	"fmt"
+	"io"
+	"log"
+	"math/big"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+)
+
+func authCode(sec string) (string, error) {
+	normalizedSec := strings.ToUpper(strings.Replace(sec, " ", "", -1))
+	key, err := base32.StdEncoding.DecodeString(normalizedSec)
+	if err != nil {
+		return "", err
+	}
+	enc := hmac.New(sha1.New, key)
+	ts := time.Now().Unix() / 30
+	msg := make([]byte, 8, 8)
+	msg[0] = (byte)(ts >> (7 * 8) & 0xff)
+	msg[1] = (byte)(ts >> (6 * 8) & 0xff)
+	msg[2] = (byte)(ts >> (5 * 8) & 0xff)
+	msg[3] = (byte)(ts >> (4 * 8) & 0xff)
+	msg[4] = (byte)(ts >> (3 * 8) & 0xff)
+	msg[5] = (byte)(ts >> (2 * 8) & 0xff)
+	msg[6] = (byte)(ts >> (1 * 8) & 0xff)
+	msg[7] = (byte)(ts >> (0 * 8) & 0xff)
+	if _, err := enc.Write(msg); err != nil {
+		return "", err
+	}
+	hash := enc.Sum(nil)
+	offset := hash[19] & 0x0f
+	trunc := hash[offset : offset+4]
+	trunc[0] &= 0x7F
+	res := new(big.Int).Mod(new(big.Int).SetBytes(trunc), big.NewInt(1000000))
+	return fmt.Sprintf("%06d", res), nil
+}
+
+func handler(w http.ResponseWriter, r *http.Request) {
+	sec := r.URL.Path[1:]
+	code, err := authCode(sec)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	if _, err := io.WriteString(w, code); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+}
+
+func main() {
+	port := os.Getenv("PORT")
+	if port == "" {
+		port = "8080"
+	}
+	http.HandleFunc("/", handler)
+	log.Fatal(http.ListenAndServe(":"+port, nil))
+}