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