Generating JWT tokens

Question

Could anyone provide me an example for generating jwt tokens with three headers given as (alg, kid, typ) that has the format:

{
  "alg": "RS256",
  "kid": "vpaas-magic-cookie-1fc542a3e4414a44b2611668195e2bfe/4f4910",
  "typ": "JWT"
}

under https://developer.8x8.com/jaas/docs/api-keys-jwt.

Jwt tokens get expired with a time limit of few hours so I am trying to find a way to generate the token in my code itself.

At the end, my javascript looks like this, where I add the jwt token inside the options list for authentication.

var options = {
                roomName: "vpaas-magic-cookie-secretKey/Room123",
                jwt: 'JWTTOKEN',
                ,

From what I have read under https://jwt.io/, I need the encoded key from the decoded details. As per the generating tokens, I think it uses HS256 algorithm. What are the steps to do this in javascript?

EDIT: After the user's answer, I did some changes to his code and I am currently generating half the JWT token. I am checking it with the already generated token on the server - Jaas.8x8

<script>
    const HMACSHA256 = (stringToSign, secret) => "not_implemented"

    // The header typically consists of two parts: 
    // the type of the token, which is JWT, and the signing algorithm being used, 
    // such as HMAC SHA256 or RSA.
    const header = {
        "kid": "vpaas-magic-cookie-07fabede3674457a84c95fsecretcode/myroom001",
        "alg": "RS256",
        "typ": "JWT"
    }
    const encodedHeaders = btoa(JSON.stringify(header))


    // create the signature part you have to take the encoded header, 
    // the encoded payload, a secret, the algorithm specified in the header, 
    // and sign that.
    const signature = HMACSHA256(`${encodedHeaders}`, "mysecret")


    console.log(`${encodedHeaders}.${signature}`)
</script>

The token that gets generated from code is

eyJraWQiOiJ2cGFhcy1tYWdpYy1jb29raWUtMDdmYWJlZGUzNjc0NDU3YTg0Yzk1ZmE4MGIxNGY1ZDcvVGVzdFJhdW0wMDEiLCJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.not_implemented

And the token that is already generated online is:

eyJraWQiOiJ2cGFhcy1tYWdpYy1jb29raWUtMDdmYWJlZGUzNjc0NDU3YTg0Yzk1ZmE4MGIxNGY1ZDcvMTg1ZDY2LVNBTVBMRV9BUFAiLCJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiJ9.eyJhdWQiOiJqaXRzaSIsImV4cCI6MTYyMDM4ODU3NiwibmJmIjoxNjIwMzgxMzcxLCJpc3MiOiJjaGF0Iiwicm9vbSI6IioiLCJzdWIiOiJ2cGFhcy1tYWdpYy1jb29raWUtMDdmYWJlZGUzNjc0NDU3YTg0Yzk1ZmE4MGIxNGY1ZDciLCJjb250ZXh0Ijp7ImZlYXR1cmVzIjp7ImxpdmVzdHJlYW1pbmciOmZhbHNlLCJvdXRib3VuZC1jYWxsIjpmYWxzZSwidHJhbnNjcmlwdGlvbiI6ZmFsc2UsInJlY29yZGluZyI6ZmFsc2V9LCJ1c2VyIjp7Im1vZGVyYXRvciI6dHJ1ZSwibmFtZSI6IlRlc3QgVXNlciIsImlkIjoiYXV0aDB8NjA5M2EyYzM3Zjc3MGEwMDcxMGE5YzY5IiwiYXZhdGFyIjoiIiwiZW1haWwiOiJ0ZXN0LnVzZXJAY29tcGFueS5jb20ifX19.aNqg_VLXyafH8Se5rThe6TLz0F2AEnJSmuoZBQ4fXEm1PMx4SBRpelJsrmL76D_jKS5NT-GkuPDVcDgLv6nx9G4ywjws1AH4Lkt0FcJ3eH2OjbFI2WxPzJF_tDJbtPme5LJmGZwEa509v2QD0r-kr31M7FZ83S-kz3O1xKc33FnMJwNlqvgCSN2S0QwF6R5J01zDk41gCk0wGr3DXAmlz0FtCU0qJ5nN9iMUpr5QUY1D-hRApWMhoLPmxkuqnQKLjGwgxU8lh33wq_Laqu7qV57lYrI27er_c42YePwuitWEAAshQU4Ylf2v8sVRv06kQdFPVvICVdsTTI-DLbc3aQ

So basically the first few strings are right but the rest is not generated. I assume it has something to do with mysecret? What exactly is this?

Answer 1

All the instructions are written on this page, https://jwt.io/introduction.

For simplicity, I did not implement HMACSHA256 or use a library to do it. You need to implement this function.

• If you want to do it from the browser, which doesn't make much sense, How to get HMAC with Crypto Web API.
• If you want to do it from node (backend), which makes more sense, you can look at this https://www.nodejsera.com/snippets/nodejs/sha256-hmac.html.

const HMACSHA256 = (stringToSign, secret) => "not_implemented"

// The header typically consists of two parts: 
// the type of the token, which is JWT, and the signing algorithm being used, 
// such as HMAC SHA256 or RSA.
const header = {
  "alg": "HS256",
  "typ": "JWT"
}
const encodedHeaders = btoa(JSON.stringify(header))


// The second part of the token is the payload, which contains the claims.
// Claims are statements about an entity (typically, the user) and 
// additional data. There are three types of claims: 
// registered, public, and private claims.
const claims = {
    "role": "admin"
}
const encodedPlayload = btoa(JSON.stringify(claims))


// create the signature part you have to take the encoded header, 
// the encoded payload, a secret, the algorithm specified in the header, 
// and sign that.
const signature = HMACSHA256(`${encodedHeaders}.${encodedPlayload}`, "mysecret")
const encodedSignature = btoa(signature)

const jwt = `${encodedHeaders}.${encodedPlayload}.${encodedSignature}`
console.log({jwt})

Note, that my answer differs from your question in that it is using HS256 instead of RS256. If you want to learn more about the difference you can take a look here: RS256 vs HS256: What's the difference?.