Node/Express Lesson 13 Coding Assignment

In this lesson, you use the passport and passport-local npm packages to handle user authentication, from within a server-side rendered application.

First Steps

You continue to work with the same repository as the previous lesson, but you create a new branch called lesson13.

The user records are stored in the Mongo database, just as for the Jobs API lesson. You have already copied the models directory tree from the Jobs API lesson into the jobs-ejs repository. The user model is used unchanged. You configure passport to use that model.

To begin, you will need the following views:

views/index.ejs
views/logon.ejs
views/register.ejs

The index.ejs view just shows links to login or register. The logon.ejs view collects the email and password from the user. The register collects the name, email, and password for a new user. We want to use the partials as well. We want to modify the header partial to give the name of the logged on user, and to add a logoff button if a user is logged on.

views/index.ejs:

<%- include("partials/head.ejs") %>
<%- include("partials/header.ejs") %>
<% if (user) { %>
    <a href="/secretWord">Click this link to view/change the secret word.</a>
<% } else { %>
    <a href="/sessions/logon">Click this link to logon.</a>
    <a href="/sessions/register">Click this link to register.</a>
<% } %>
<%- include("partials/footer.ejs") %>

views/logon.ejs:

<%- include("partials/head.ejs") %>
<%- include("partials/header.ejs") %>
<form method="POST">
  <div>
    <label name="email">Enter your email:</label>
    <input name="email" />
  </div>
  <div>
    <label name="password">Enter your password:</label>
    <input type="password" name="password" />
  </div>
  <div>
    <button>Logon</button>
    <a href="/">
      <button type="button">Cancel</button>
    </a>
  </div>
</form>
<%- include("partials/footer.ejs") %>

views/register.js

<%- include("partials/head.ejs") %>
<%- include("partials/header.ejs") %>
<form method="POST">
  <div>
    <label name="name">Enter your name:</label>
    <input name="name" />
  </div>
  <div>
    <label name="email">Enter your email:</label>
    <input name="email" />
  </div>
  <div>
    <label name="password">Enter your password:</label>
    <input type="password" name="password" />
  </div>
  <div>
    <label name="password1">Confirm your password:</label>
    <input type="password" name="password1" />
  </div>
  <div>
    <button>Register</button>
    <a href="/">
      <button type="button">Cancel</button>
    </a>
  </div>
</form>
<%- include("partials/footer.ejs") %>

Revised views/partials/header.ejs:

<h1>The Jobs EJS Application</h1>
<% if (user) { %>
   <p>User <%= user.name %> is logged on.</p>
   <form method="POST" action="/sessions/logoff">
   <button>Logoff</button>
   </form>
<% } %>
<% if (errors) {
    errors.forEach((err) => { %>
      <div>
        Error: <%= err %>
      </div>
    <% })
  } %>
  <% if (info) {
    info.forEach((msg) => { %>
      <div>
        Info: <%= msg %>
      </div>
    <% })
  } %>
<hr />

These changes won’t suffice to do anything in the application, until routes are added to match. We need to follow best practices, with separate route and controller files.

Router and Controller

Create a file routes/sessionRoutes.js, as follows:

const express = require("express");
// const passport = require("passport");
const router = express.Router();

const {
  logonShow,
  registerShow,
  registerDo,
  logoff,
} = require("../controllers/sessionController");

router.route("/register").get(registerShow).post(registerDo);
router
  .route("/logon")
  .get(logonShow)
  .post(
    // passport.authenticate("local", {
    //   successRedirect: "/",
    //   failureRedirect: "/sessions/logon",
    //   failureFlash: true,
    // })
    (req, res) => {
      res.send("Not yet implemented.");
    }
  );
router.route("/logoff").post(logoff);

module.exports = router;

Ignore the passport lines for the moment. This just sets up the routes. We need to create a corresponding file controllers/sessionController.js. Here we use the User model. However, the file you copied makes some references to the JWT library. You must edit models/User.js to remove those references in order for User.js to load. We aren’t using JWTs in this project.

const User = require("../models/User");
const parseVErr = require("../util/parseValidationErr");

const registerShow = (req, res) => {
  res.render("register");
};

const registerDo = async (req, res, next) => {
  if (req.body.password != req.body.password1) {
    req.flash("error", "The passwords entered do not match.");
    res.render("register");
  }
  try {
    await User.create(req.body);
  } catch (e) {
    if (e.constructor.name === "ValidationError") {
      parseVErr(e, req);
    } else if (e.name === "MongoServerError" && e.code === 11000) {
      req.flash("error", "That email address is already registered.");
    } else {
      return next(e);
    }
    return res.render("register");
  }
  res.redirect("/");
};

const logoff = (req, res) => {
  req.session.destroy(function (err) {
    if (err) {
      console.log(err);
    }
    res.redirect("/");
  });
};

const logonShow = (req, res) => {
  if (req.user) {
    return res.redirect("/");
  }
  res.render("logon", {
    errors: req.flash("error"),
    info: req.flash("info"),
  });
};

module.exports = {
  registerShow,
  registerDo,
  logoff,
  logonShow,
};

We have two endpoints that handle just rendering an EJS page, registerShow and logonShow.

We then have endpoints for actually performing the logoff and register actions. We don’t need a controller handler for login, because Passport handles that for us.

The registerDo handler will check if the two passwords the user entered match, and refresh the page otherwise. If all is good there, it will create a user in the database and redirect to the home page. The creation of the user entry in Mongo is just the same as it was for the Jobs API. We also have some error handling cases here.

If there is a Mongoose validation error when creating a user record, we need to parse the validation error object to return the issues to the user in a more helpful format, and we do that in the file util/parseValidationErrs.js:

const parseValidationErrors = (e, req) => {
  const keys = Object.keys(e.errors);
  keys.forEach((key) => {
    req.flash("error", key + ": " + e.errors[key].properties.message);
  });
};

module.exports = parseValidationErrors;

We need some middleware to load res.locals with any variables we need, like the logged in user and flash properties. Create middleware/storeLocals.js:

const storeLocals = (req, res, next) => {
  if (req.user) {
    res.locals.user = req.user;
  } else {
    res.locals.user = null;
  }
  res.locals.info = req.flash("info");
  res.locals.errors = req.flash("error");
  next();
};

module.exports = storeLocals;

Now, we need a couple of app.use statements. Add these lines right after the connect-flash line:

app.use(require("./middleware/storeLocals"));
app.get("/", (req, res) => {
  res.render("index");
});
app.use("/sessions", require("./routes/sessionRoutes"));

We are now using the database. So, we need to connect to it at startup. You need a file, db/connect.js. Check that it looks like the following:

const mongoose = require("mongoose");

const connectDB = (url) => {
  return mongoose.connect(url, {});
};

module.exports = connectDB;

Then add this line to app.js, just before the listen line:

await require("./db/connect")(process.env.MONGO_URI);

Then try the application out, starting at the "/" URL. You can try each of the new views. But you still can’t logon. The logon operation is commented out, because Passport is not set up.

Configuring Passport

To use Passport, you have to tell it how to authenticate users, retrieving them from the database. Create a file passport/passportInit.js, as follows:

const passport = require("passport");
const LocalStrategy = require("passport-local").Strategy;
const User = require("../models/User");

const passportInit = () => {
  passport.use(
    "local",
    new LocalStrategy(
      { usernameField: "email", passwordField: "password" },
      async (email, password, done) => {
        try {
          const user = await User.findOne({ email: email });
          if (!user) {
            return done(null, false, { message: "Incorrect credentials." });
          }

          const result = await user.comparePassword(password);
          if (result) {
            return done(null, user);
          } else {
            return done(null, false, { message: "Incorrect credentials." });
          }
        } catch (e) {
          return done(e);
        }
      }
    )
  );

  passport.serializeUser(async function (user, done) {
    done(null, user.id);
  });

  passport.deserializeUser(async function (id, done) {
    try {
      const user = await User.findById(id);
      if (!user) {
        return done(new Error("user not found"));
      }
      return done(null, user);
    } catch (e) {
      done(e);
    }
  });
};

module.exports = passportInit;

Here we are registering a “strategy” to tell Passport how to handle requests that we pass to it. passport.use is a function that takes the name you want to give this passport strategy (here we’re using "local") and the strategy as the second argument, where we’re passing in a new LocalStrategy from the passport-local library.

The LocalStrategy constructor takes two arguments: an options object, and a callback function. The options object expects us to tell the strategy what field on the request will have the user identifier, and what field will have the password. Here, we tell it to look for "email" as the identifier, and password for the password.

The second argument passed to the LocalStrategy constructor is the callback function that will be called when we do passport.authenticate(...) in the login route in sessionRoutes.js. The local-strategy library will extract the email and password fields that we defined in the options/first argument, from the req.body. If it doesn’t find those fields, it will return a 400 error. If it does find them, then it will then pass those (along with a done callback) to the function we’ve defined above. It’s up to us then to write the code specific to our application, that handles checking if the user exists and has used to correct password.

The done callback accepts three arguments:

  1. An error, if there is one, otherwise just pass in null
  2. The user object, if the user is found and used valid credentials, otherwise false
  3. An object with a message property and type, this can be used in both error and success cases to show flash messages. Here we’e only using it in non-error failure cases (user not found or wrong credentials used).

In addition to registering our local strategy, we also define serializeUser and deserializeUser functions on the passport object.

serializeUser is used when saving a user to the request session object. We can’t save an object to the session cookie, so we need to “serialize” it a.k.a. encode it as a string. In the above function, we’re doing that by telling Passport to save just the user id to the session cookie.

Then when Passport is handling a protected route, it will use the deserializeUser function to retrieve the user from the database, using the id that was saved to the session cookie.

You can now add the following lines to app.js, right after the app.use for session (Passport relies on session):

const passport = require("passport");
const passportInit = require("./passport/passportInit");

passportInit();
app.use(passport.initialize());
app.use(passport.session());

First we call the passportInit function that we created in the previous section. This registers our local Passport strategy, and sets up the serializeUser and deserializeUser functions onto the passport object.

Then we call passport.initialize() (which sets up Passport to work with Express and sessions) and passport.session() (which sets up an Express middleware that runs on all requests, checks the session cookie for a user id, and if it finds one, deserializes and attaches it to the req.user property).

Finally, you can now uncomment the lines having to do with Passport in routes/sessionRoutes.js, so that the require statement for Passport is included, and so that the route for logon looks like

router
  .route("/logon")
  .get(logonShow)
  .post(
    passport.authenticate("local", {
      successRedirect: "/",
      failureRedirect: "/sessions/logon",
      failureFlash: true,
    })
  );

This means that when someone sends a POST request to the /sessions/logon path, Passport will call the function we defined earlier and registered to the name "local". If that function completes successfully (done(...) is called with no error argument), then it will redirect the page to the successRedirect page. If there is an error, then it will redirect to the failureRedirect page, and also set a flash message with the message property from the object we passed to done(...).

Since we’re letting Passport handle setting the req.flash properties now, we can remove the lines in routes/sessionController.js that set the flash messages for the loginShow handler. So that should now just look like:

const logonShow = (req, res) => {
  if (req.user) {
    return res.redirect("/");
  }
  res.render("logon");
};

After that, try logon for one of the accounts you have created. You should see that you are logged in and can access the secretWord page. You should also see appropriate error messages for bad logon credentials. Also, test logoff.

Protecting a Route

To protect a route, you need some middleware, as follows.

middleware/auth.js:

const authMiddleware = (req, res, next) => {
  if (!req.user) {
    req.flash("error", "You can't access that page before logon.");
    res.redirect("/");
  } else {
    next();
  }
};

module.exports = authMiddleware;

req.user is injected into the req object by passport.session(). We can check if it exists (a.k.a. if the user is logged-in) in this middleware and use that to determine if the non-logged-in requester should be redirected to the home page, or if the logged-in user should be allowed to continue to the next middleware or controller handler function.

We want to protect any route for the "/secretWord" path. The best practice is to put the code for those routes into a router file, as follows.

routes/secretWord.js:

const express = require("express");
const router = express.Router();

router.get("/", (req, res) => {
  if (!req.session.secretWord) {
    req.session.secretWord = "syzygy";
  }

  res.render("secretWord", { secretWord: req.session.secretWord });
});

router.post("/", (req, res) => {
  if (req.body.secretWord.toUpperCase()[0] == "P") {
    req.flash("error", "That word won't work!");
    req.flash("error", "You can't use words that start with p.");
  } else {
    req.session.secretWord = req.body.secretWord;
    req.flash("info", "The secret word was changed.");
  }

  res.redirect("/secretWord");
});

module.exports = router;

We could further refactor this by moving the code for handling the routes ((req, res) => {...}) a controller file, like we’ve done for the session routes, but we’ll leave it like this for now.

Next let’s replace the app.get and app.post statements for the "/secretWord" routes in app.js with these lines:

const secretWordRouter = require("./routes/secretWord");
app.use("/secretWord", secretWordRouter);

Then try out the secretWord page to make sure it still works. Turning on protection is simple. You add the authentication middleware to the route above as follows:

const auth = require("./middleware/auth");
app.use("/secretWord", auth, secretWordRouter);

That causes the authentication middleware to run before the secretWordRouter, and it redirects if any requests are made for those routes before logon. Try it out: login and verify that you can see and change the secretWord. Then logoff and try to go to the "/secretWord" URL.

Fixing the Security

Passport is using the session cookie to determine if the user is logged in. This creates a security vulnerability called “cross site request forgery” (CSRF). We will demonstrate this.

To see this, clone this repository into a separate directory, outside of the current jobs-ejs folder. Then, within the directory you cloned, install packages with npm install and run the app with node app. This will start another express application listening on port 4000 of your local machine. This is the attacking code. It could be running anywhere on the Internet — that has nothing to do with the attack.

You should have two browser tabs open, one for localhost:3000, and one for localhost:4000. The one at localhost:4000 just shows a button that says Click Me! Don’t click it yet. Use the jobs-ejs application in the 3000 tab to set the secret string to some value. Then log off. Then click the button in the 4000 tab. Then log back on in the 3000 tab and check the value of the secret string. So far so good — it still has the value you set.

Now, without logging off of jobs-ejs , click the button in the 4000 tab. Then refresh the /secretWord page in jobs-ejs. Hey, what happened! (By the way, this attack would succeed even if you closed the 3000 tab entirely.)

You see, the other application sends a request to your application in the context of your browser — and that browser request automatically includes the cookie. So, the application thinks the request comes from a logged on user, and honors it. If the application, as a result of a form post, makes database changes, or even transfers money, the attacker could do that as well.

So, how to fix this? This is the purpose of the host-csrf package you installed at the start of the project. Follow the instructions here to integrate the package with your application. You will need to change app.js as well as each of the forms in your EJS files. You can use process.env.SESSION_SECRET as your cookie-parser secret. Note that the app.use for the CSRF middleware must come after the cookie parser middleware and after the body parser middleware, but before any of the routes. You will see a message logged to the console that the CSRF protection is not secure. That is because you are using HTTP, not HTTPS, so the package is less secure in this case, but you would be using HTTPS in production. As you will see, it stops the attack.

Re-test, first to see that your application still works, and second, to see that the attack no longer works. (A moral: Always log off of sensitive applications before you surf, in case the sensitive application is vulnerable in this way. Also note that it does not help to close the application, as the cookie is still present in the browser. You have to log off to clear the cookie. Even restarting the browser does not suffice.)

Enabling CSRF protection in the project is an important part of this lesson — don’t omit it! By the way, the CSRF attack only works when the credential is in a cookie. It doesn’t work if you use JWTs in the authorization header. There are advantages and disadvantages to both forms of sending protected data between a client and a server.

Submitting Your Work

As usual, add and commit your changes and push the lesson13 branch to your Github. Then create the pull request and include the link in your homework submission.

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