auth-service.js

const jwt = require('jsonwebtoken');

module.exports = {
  authenticate: (email, password) => {
    let user;

    // Implement the credential validation however you'd like.
    if (email.length && password.length) {
      user = {
        id: 1,
        roles: ["admin"]
      }
    }

    if (!user) throw new Error("Invalid credentials.");

    return jwt.sign(user, process.env.JWT_SECRET);
  },
  validateToken: token => {
    try {
      const { id, roles } = jwt.verify(token, process.env.JWT_SECRET);
      return { id, roles };
    } catch (e) {
      throw new Error('Authentication token is invalid.');
    }
  }
}