Middleware.js

var jwt = require("jsonwebtoken");

var authPage = function authPage(roles) {
  return function (req, res, next) {
    var token = req.headers.authorization.split(" ")[1];
    token = token.replace("Bearer ", "");

    console.log(token);
    var decoded = jwt.verify(token, "secret");
    var userRole = decoded.role;

    if (roles.includes(userRole)) {
      next();
    } else {
      res.status(401).json({
        message: "Unauthorized",
      });
    }
  };
};

module.exports = { authPage: authPage };

The middleware.js file exports a middleware function named authPage. This function takes in an array of roles and returns a middleware function that checks the authorization of the incoming request. It retrieves the token from the request headers, verifies it using the "secret" key, and checks if the decoded role is included in the allowed roles. If the role is allowed, it calls next() to proceed to the next middleware or route handler. Otherwise, it sends a 401 Unauthorized response.

---

Index.js

const express = require("express");
const { authPage } = require("./middleware");
const cors = require("cors");
const app = express();
const jwt = require("./jwt");
app.use(cors());
app.use(express.json());

app.get("/course/grades", authPage(["teacher", "admin"]), (req, res) => {
  res.json({
    nimal: 80,
    kamal: 90,
    sunil: 70,
  });
});

app.get("/", (req, res) => {
  res.json({ token: jwt.token });
});

app.listen(3001, () => {
  console.log("Server listening on port 3001");
});

The index.js file sets up an Express server. It imports the authPage middleware function from the middleware.js file and the jwt token from the jwt.js file. The server uses the cors middleware and parses incoming requests as JSON.

There are two routes defined:

• The /course/grades route uses the authPage middleware to check if the request is authorized for the roles "teacher" or "admin". If authorized, it sends a JSON response with course grades for some students.
• The root route / sends a JSON response containing the jwt token.

The server listens on port 3001.

---

jwt.js

var jwt = require("jsonwebtoken");

var token = jwt.sign(
  {
    exp: Math.floor(Date.now() / 1000) + 60 * 60,
    role: "admin",
  },
  "secret"
);

exports.token = token;

The jwt.js file generates a JWT (JSON Web Token) using the jsonwebtoken library. The token is signed with a payload containing an expiration time (exp) and a role (role). In this case, the role is set to "admins". The token is exported to be used in other parts of the application.