How to generate RSA SHA256 signature by Javascript

[Nalini Shrma]

Hi,

I want to generate RSA SHA256 token based on jwt.io by javascript. Is there any source code or anything or available. 

Regards

[Nalini Shrma]

Hi,

I want to generate RSA SHA256 token based on jwt.io by javascript. Is there any source code or anything or available.

Regards,  

[Ben Turner]

Why not just use the jwt.io library https://jwt.io/#libraries-io

[dorian_...@wrdsb.ca]

Did you have any luck accomplishing this? I'm trying to do something similar/same, I want to get an oauth2 access token for a google service account so that I can then make calls to the gmail api. However after forming the JWT to post to the oauth endpoint all I get is Invalid signature. I have a stackoverflow question up right now that goes into more detail than this post with some of my code. You can see it here: https://stackoverflow.com/questions/46221972/nodejs-post-request-to-get-oauth2-token-for-a-service-account

Did you get it to work?

[Jaret Flores]

So certainly there are libraries for this as @Nalini points out.

Here is some Node.js sample code that may present some ideas you can use.  Warning: I have not run the code nor do I advocate that it replicates JWT, but it's looks like something I would start with if I were to try to implement it.

const crypto = require('crypto');

const header = { alg: 'HS256', typ: 'JWT' },

    data = { a: 1 b: 2 },

    secret = 'secret';

assert(isValidJwt(makeJwt(header, data, secret), secret));

function makeJwt (header, data, secret) {
    const base64Header = objToBase64(header);
        base64Data = objToBase64(data),
        base64Signature = jwtSignature(base64Header, base64Data, secret);

    return base64Header + '.' + base64Data + '.' base64Signature;
}

function isValidJwt (jwt, secret) {
    const [base64Header, base64Data, base64Signature] = jwt.split('.');

    return base64Signature === jwtSignature(base64Header, base64Data, secret);
}

function jwtSignature (base64Header, base64Data, secret) {
    return crypto
        .createHmac('sha256', secret)
        .update(base64Header + '.' + base64Data)
        .digest('base64');
}

function objToBase64 (obj) {
    return Buffer.from(JSON.stringify(obj), 'utf8').toString('base64');
}

[Nagesh Kumar]

You seem to have RSA and DSA confused. However, if you want to sign using RSA-sha256, then use the EVP interface for signing. You can initialize with the EVP_SignInit_ex() method with EVP_sha256() for the type argument.

thank you

Nagesh kumar