Where to store the JWT Client Credentials Grant

Question

I have a NodeJS Express Application that authenticates to an Auth Server via client credentials grant. The token that I receive is used to load data from an API.

What is the best practice to store the token across the application?

Note that the JWT is not user specific, since my Express App is the Client.

Answer 1

I will store it in memory. Normally I will write a singleton module to handle it.

auth.js:

class Auth {
    getToken() {
        // check if we has token already and that token isn't expired
        if (this.token && !isExpired(this.token)) {
            return Promise.resolve(this.token);
        }
        // if not we call API for the new token then return the new token
        return asyncCallApiForToken();
    }
}
module.exports = new Auth();

main.js

const auth = require('./auth.js)

auth.getToken()
    .then(token => {
        // we got token here
    }

Answer 2

I'd try to avoid persisting the returned token and only keep it in-memory, as the client credentials grant enables you to fetch a new token relatively easily, and without user interaction.

But if that's problematic, then I'd say: Next to the client credentials, since the client credentials are at least as sensitive as the JWT token.