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main.go
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main.go
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package main
import (
"crypto/hmac"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"encoding/hex"
"encoding/json"
"encoding/pem"
"errors"
"fmt"
"log"
"net/http"
"os"
"strings"
"github.com/fernet/fernet-go"
wxas "github.com/darrenparkinson/wxa-skills-go"
)
type payload struct {
Signature string `json:"signature"`
Message string `json:"message"`
}
type config struct {
publicKey string
secret string
}
func main() {
cfg := loadEnv()
message := generateJSONMessage()
payloadJSON, err := preparePayload(message, cfg)
if err != nil {
log.Fatal(err)
}
resp, err := http.Post("http://localhost:8080", "application/json", strings.NewReader(payloadJSON))
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
log.Println("Status:", resp.Status)
log.Println("Response:")
var result wxas.WebexAssistantResponse
err = json.NewDecoder(resp.Body).Decode(&result)
if err != nil {
log.Fatal(err)
}
jres, err := json.MarshalIndent(result, " ", " ")
if err != nil {
log.Fatal(err)
}
fmt.Println(string(jres))
}
// preparePayload returns the json string required to send to the skill, simulating webex assistant
func preparePayload(message string, cfg config) (string, error) {
var result payload
token, err := generateToken(message, cfg.publicKey)
if err != nil {
return "", err
}
signature := signToken(token, cfg.secret)
if err != nil {
return "", err
}
result.Signature = signature
result.Message = token
resultJSON, err := json.MarshalIndent(result, " ", " ")
if err != nil {
return "", err
}
return string(resultJSON), nil
}
// generateToken takes a plaintext message and a public key. It uses a fernet key to encrypt
// the message and encrypts the fernet key with the public key. It returns the encrypted fernet
// key and the encrypted message each individually base64 encoded and separated by a ".".
// IKR 🙄
func generateToken(message string, publicKey string) (string, error) {
var fernetKey fernet.Key
err := fernetKey.Generate()
if err != nil {
return "", err
}
encryptedMessage, err := fernet.EncryptAndSign([]byte(message), &fernetKey)
if err != nil {
return "", err
}
encodedEncryptedFernetKey, err := encryptFernetKey(fernetKey.Encode(), publicKey)
if err != nil {
return "", err
}
encodedEncryptedMessage := base64.StdEncoding.EncodeToString(encryptedMessage)
return fmt.Sprintf("%s.%s", encodedEncryptedFernetKey, encodedEncryptedMessage), nil
}
func encryptFernetKey(fernetKey string, publicKey string) (string, error) {
block, _ := pem.Decode([]byte(publicKey))
if block.Type != "PUBLIC KEY" {
return "", errors.New("error decoding public key from pem")
}
parsedKey, err := x509.ParsePKIXPublicKey(block.Bytes)
if err != nil {
return "", fmt.Errorf("error parsing public key: %s", err)
}
var ok bool
var pubkey *rsa.PublicKey
if pubkey, ok = parsedKey.(*rsa.PublicKey); !ok {
return "", errors.New("unable to parse public key")
}
rng := rand.Reader
ciphertext, err := rsa.EncryptOAEP(sha256.New(), rng, pubkey, []byte(fernetKey), nil)
if err != nil {
return "", err
}
return base64.StdEncoding.EncodeToString(ciphertext), nil
}
func signToken(token string, secret string) string {
mac := hmac.New(sha256.New, []byte(secret))
mac.Write([]byte(token))
signature := mac.Sum(nil)
return base64.StdEncoding.EncodeToString(signature)
}
func loadEnv() config {
pub, err := os.ReadFile("public.pem")
if err != nil {
log.Fatal(err)
}
secret, err := os.ReadFile("secret.txt")
if err != nil {
log.Fatal(err)
}
cfg := config{
publicKey: string(pub),
secret: string(secret),
}
if cfg.publicKey == "" || cfg.secret == "" {
log.Fatal("missing environment variables")
}
return cfg
}
func generateJSONMessage() string {
challenge, _ := generateChallenge()
message := wxas.WebexAssistantMessage{
// Text: []string{"Hello World."},
Text: "Hello World.",
Challenge: challenge,
}
j, _ := json.MarshalIndent(message, " ", " ")
return string(j)
}
func generateChallenge() (string, error) {
b := make([]byte, 32)
_, err := rand.Read(b)
if err != nil {
return "", err
}
return hex.EncodeToString(b), nil
}