JWT Encoder

async function signJWT(payload, secret, alg = 'HS256') {
  const header = { alg, typ: 'JWT' }
  const enc = new TextEncoder()

  // Base64url encode header and payload
  const b64url = (obj) =>
    btoa(JSON.stringify(obj)).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '')

  const h = b64url(header)
  const p = b64url(payload)

  // Sign with HMAC-SHA256
  const key = await crypto.subtle.importKey(
    'raw', enc.encode(secret),
    { name: 'HMAC', hash: 'SHA-256' }, false, ['sign']
  )
  const sig = await crypto.subtle.sign('HMAC', key, enc.encode(`${h}.${p}`))
  const s = btoa(String.fromCharCode(...new Uint8Array(sig)))
    .replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '')

  return `${h}.${p}.${s}`
}

// Usage
const token = await signJWT(
  { sub: 'user-123', name: 'Alice', iat: Math.floor(Date.now() / 1000) },
  'your-256-bit-secret'
)
// → "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOi..."

import jwt
import time

payload = {
    "sub": "user-123",
    "name": "Alice",
    "iat": int(time.time()),
    "exp": int(time.time()) + 3600,  # expires in 1 hour
}

# Sign with HS256 (default)
token = jwt.encode(payload, "your-256-bit-secret", algorithm="HS256")
# → "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOi..."

# Verify and decode
decoded = jwt.decode(token, "your-256-bit-secret", algorithms=["HS256"])
# → {"sub": "user-123", "name": "Alice", "iat": 1717200000, "exp": 1717203600}

const jwt = require('jsonwebtoken')

const payload = {
  sub: 'user-123',
  name: 'Alice',
  role: 'admin',
}

// Sign — iat is added automatically
const token = jwt.sign(payload, 'your-256-bit-secret', {
  algorithm: 'HS256',
  expiresIn: '1h',    // sets exp claim
  issuer: 'auth.example.com',  // sets iss claim
})

// Verify
const decoded = jwt.verify(token, 'your-256-bit-secret')
// → { sub: 'user-123', name: 'Alice', role: 'admin', iat: ..., exp: ... }

package main

import (
    "fmt"
    "time"
    "github.com/golang-jwt/jwt/v5"
)

func main() {
    claims := jwt.MapClaims{
        "sub":  "user-123",
        "name": "Alice",
        "iat":  time.Now().Unix(),
        "exp":  time.Now().Add(time.Hour).Unix(),
    }

    token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
    signed, _ := token.SignedString([]byte("your-256-bit-secret"))
    fmt.Println(signed)
    // → eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOi...
}