Getting an Einstein (Metamind) auth token

einstein_authtoken.js

const jwt = require('jsonwebtoken');
const request = require('request');

const url = 'https://api.metamind.io/';
const account_id = '<SNIP>';
const private_key = `-----BEGIN RSA PRIVATE KEY-----
<SNIP>
-----END RSA PRIVATE KEY-----
`;

const reqUrl = `${url}v1/oauth2/token`;

// JWT payload
const rsa_payload = {
    'sub': account_id,
    'aud': url
};

const rsa_options = {
    header: {
        'alg': 'RS256',
        'typ': 'JWT'
    },
    expiresIn: '1h'
};

// Sign the JWT payload
const assertion = jwt.sign(
    rsa_payload,
    private_key,
    rsa_options
);

const options = {
    url: reqUrl,
    headers: {
        'Content-Type': 'application/x-www-form-urlencoded',
        'accept': 'application/json'
    },
    body: `grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer&assertion=${encodeURIComponent(assertion)}`
};

// Make the OAuth call to generate a token
request.post(options, (error, response, body) => {
    //   var data = JSON.parse(body);
    //   console.log(data['access_token']);
    console.log(body);
});