Implementing Authorization in JavaScript with Express.js and MongoDB

If you've followed our previous article on authentication, first off, thank you! Now, it's time to take our understanding a step further and dive into the world of authorization, an area that's as crucial as authentication, yet distinctly unique.

A Quick Refresher on Our Authentication Journey

In our previous article, we laid down the foundation of understanding user identification, and we explored how to securely register users, ensure they are who they say they are, and use JWTs to verify their interactions. 

Laying the Ground for Authorization

At its core, authorization is simply about permissions, or look at it as the logic and rules that determine what actions a user can perform in an application, based on their identity and, often, other factors.

Whether it's allowing a regular user to view content, an author to edit their articles, or an admin to manage user accounts, authorization governs these decisions.

Roles and Permissions: Building a Structured Access Framework

When it comes to determining what a user can and cannot do within an application, roles, and permissions form the bedrock of our authorization strategies.

The Essence of Roles

Roles are broad categories or labels that we assign to users, representing their position or function within an application, and common examples you might have encountered include roles like 'user', 'admin', or 'moderator'.

A role is, in essence, a collection of permissions bundled under a descriptive name. For instance, an 'admin' might have permission to add or remove content, manage user accounts, and view system settings, while a regular 'user' might only view content.

Drilling Down to Permissions

Permissions represent specific actions or tasks a user can perform, where they're the granular, often binary decisions: can a user read this article? Can they delete this comment?

Permissions can be simple, like 'read', 'write', or 'delete', but they can also be more specific, such as 'edit_own_content' or 'view_user_data'. As you can guess, with clear-cut permissions, we can tailor the user experience and ensure that users only access what they're supposed to.

The Significance of Clear Role and Permission Boundaries

Establishing well-defined roles and permissions is more than just an organizational task; remember it's about security, and it’s a fundamental aspect.

When we're explicit about what each role can do and what permissions they have, it reduces ambiguities and potential security loopholes, and there's a principle in security known as the "Principle of Least Privilege", which asserts to give users only the permissions they need to perform their tasks, and demarcating roles and permissions ensures that users don't accidentally get more access than they should.

As we move forward, we'll be looking at how to implement these roles and permissions effectively, ensuring both functionality and security for our application.

Implementing Role-based Authorization

Role-based authorization, often abbreviated as RBAC, is a popular approach to structuring permissions, and thanks to it we assign roles to users and then define what each of those roles can do. Let's see how we can put this into action with Express.js and MongoDB.

Assigning Roles to Users

Whether during registration or later, there comes a time when we must decide on a user's role; here's a simple way to assign a role during the registration process using Express.js and MongoDB (let’s use the same User schema we defined in the previous authentication article):

const express = require('express');
const User = require('./models/User'); // Assuming you have a User model

const router = express.Router();

router.post('/register', async (req, res) => {
  try {
    const user = new User({
      username: req.body.username,
      password: req.body.password,
      role: 'user' // Default role
    });
    await user.save();
    res.status(201).send({ message:
'User registered successfully!' });
  } catch (error) {
   
res.status(500).send(error.message
;
  }
});

Checking Roles Using Middleware

Middleware functions in Express.js are excellent for executing code before our main route handlers, so we can use middleware to check if a user has the right role. Here's a simple middleware to ensure that only admins access specific routes:

function ensureAdmin(req, res, next) {
  if (req.user && req.user.role === 'admin') {
    return next();
  }
  res.status(403).send('Access denied. Admins only.');
}

// Then use the middleware
router.get('/admin-dashboard', ensureAdmin, (req, res) => {
  // Handle the admin dashboard view
});

Role Inheritance

In some systems, roles might have a hierarchical structure. A 'moderator', for example, might have all the rights of a regular 'user', plus some additional permissions, so instead of duplicating permissions, we can build on existing roles; here's a conceptual example:

const roles = {
  user: ['read'],
  moderator: ['read', 'edit', 'delete_own_content'],
  admin: ['read', 'edit', 'delete_any_content', 'manage_users']
};

In this model, if a route requires 'read' permission, both the user and admin roles would qualify.

Dynamic and Attribute-based Authorization

Role-based authorization offers a structured approach to defining what users can do based on their roles. However, sometimes we need more granularity and flexibility in our authorization mechanisms, and here dynamic and attribute-based authorization help us.

Moving Beyond Roles

Roles are an excellent starting point, but they might not capture every nuance of our application; for instance, consider a blogging platform, where a user role might allow someone to create a post: how do we make sure that only the author of that post can edit or delete it?

router.put('/edit-post/:postId', async (req, res) => {
  const post = await Post.findById(req.params.postId);

  if (req.user.id !== post.authorId) {
    return res.status(403).send('Access denied. Only the author can edit.');
  }

  // Continue with the edit logic
});

Attribute-based Authorization

Attribute-based authorization (ABAC) considers various attributes: user attributes, action attributes, and environmental attributes; for instance, consider a scenario where only users from a certain region can view content, or content can be edited only during certain times of the day.

function canEditContent(user, content, currentTime) {
  return user.role === 'editor' &&
         user.region === 'US' &&
         (8 <= currentTime.getHours() && currentTime.getHours() <= 17);
}

router.put('/edit-content/:contentId', (req, res) => {
  const currentTime = new Date();

  if (!canEditContent(req.user, req.content, currentTime)) {
    return res.status(403).send('Access denied. Check your permissions or the editing time window.');
  }

  // Continue with editing logic
});

Context-aware Authorization

Sometimes, the context in which an action occurs is as crucial as the action itself; for example, a user might be able to delete their comments, but only within 24 hours of posting.

router.delete('/delete-comment/:commentId', async (req, res) => {
  const comment = await Comment.findById(req.params.commentId);

  const timeElapsed = Date.now() - new Date(comment.createdAt).getTime();
  const oneDayInMilliseconds = 24  60  60 * 1000;

  if (timeElapsed > oneDayInMilliseconds) {
    return res.status(403).send('Access denied. You can only delete your comments within 24 hours of posting.');
  }

  // Proceed with deletion logic
});

Dynamic and attribute-based authorization methods offer a high degree of customization.

You can be sure that our application's authorization logic aligns closely with our business requirements and with a combo of these techniques with role-based authorization, we can craft a comprehensive and robust authorization system that scales with our application's complexity.

Bridging Backend Authorization with User Experience

After setting up a detailed authorization system on the backend, it's essential to synchronize this logic with the front end to provide a seamless user experience. We don't want users trying to access features they're not entitled to only to be hit with errors.

Requesting Role or Permission Data

To determine which features and options to display to a user, the front end often needs to be aware of the user's roles or permissions. It can be achieved with an API endpoint:

router.get('/user-permissions', (req, res) => {
  const user = req.user; // Assuming user is attached to the request
  res.json({ permissions: user.permissions });
});

On the front end, after logging in, you might make a call to this endpoint and then store the permissions in the application's state.

Displaying Content Based on User Permissions

With the permissions available on the front, conditional rendering can be used to show or hide features; using a frontend framework like React, this can look like this:

function DeleteButton() {
  const { permissions } = useContext(UserContext);

  if (!permissions.includes('delete')) {
    return null; // Don't render the button if the user lacks the 'delete' permission
  }

  return <button>Delete</button>;
}

Handling Authorization Failures

Despite our best efforts, there might be times when a user tries to perform an unauthorized action, perhaps due to outdated permission data on the front end, and it's really important to handle these cases gracefully:

• Prompting the User: If a user's action is denied, a user-friendly message can inform them of the denial reason.

• Refreshing Permission Data: In some cases, you might choose to re-fetch the user's permissions if an authorization failure occurs to ensure the front end is in sync with the backend.

• Redirecting: For more severe breaches, such as trying to access an admin-only section, you could redirect the user to a different page or even log them out.

For example, handling a 403 Forbidden response in a fetch call:

fetch('/admin-data')
  .then(response => {
    if (response.status === 403) {
      alert('You do not have permission to access this data.');
      // Handle redirection or other responses here
    }
    return response.json();
  })
  .then(data => {
    // Handle data if fetched successfully
  });

Navigating the Tricky Waters of Authorization

Authorization is not just about setting up a system but ensuring its continued reliability and integrity.

Even with the best initial setup, there are common pitfalls that developers can fall into, and keep in mind that knowing these and the best practices to counteract them can save a lot of future headaches.

Addressing Common Mistakes in Implementing Authorization

• Overly Broad Permissions: Granting permissions that are too broad can expose more data than necessary, so always adopt the principle of least privilege—only give permissions that are strictly required for a task.

• Hardcoding Roles and Permissions: It might be tempting to hardcode roles or permissions, especially in smaller applications, but as the application grows or requirements change, this can become a significant limitation.

• Not Updating Permissions: Just as it's crucial to add permissions when introducing new features, it's equally important to remove or update permissions if a feature is deprecated.
  
  

Best Practices for Maintaining and Updating Authorization Logic

• Regular Audits: Periodically review and audit your authorization logic and ensure that it aligns with the current requirements and that there are no security loopholes.

• Use Middleware Effectively: In frameworks like Express.js, middleware offers a clean way to handle authorization, so remember to order middleware correctly, so authentication happens before authorization.

• Stay Updated: Libraries and frameworks evolve, often addressing vulnerabilities or introducing more efficient methods, and with that in mind regularly update your tools and stay informed about changes.

// Avoid hardcoding roles directly in your code
const isAdmin = (user) => user.role === 'admin'; // Not recommended

// Instead, consider using a configuration or a database to manage roles and permissions
const rolesConfig = {
  admin: {
    canDelete: true,
    canEdit: true,
    // ... other permissions
  },
  // ... other roles
};

const canUserEdit = (user) => rolesConfig[user.role]?.canEdit;

Security Considerations Specifically Related to Authorization

• Session Hijacking: Ensure that session management is secure because an attacker with access to a user's session can bypass authorization checks.

• Permission Escalation: Be wary of endpoints that can change a user's permissions, and these need to be highly secure to prevent unauthorized role escalation.

• Feedback Loop: Be cautious about the feedback you provide to unauthorized users, so telling an unauthorized user explicitly why they can't access something might give away more information than you intend.
  
  
  

Conclusion: Staying Vigilant in a Changing Landscape

Authorization, while technical, is fundamentally about trust, trusting users with access to resources, and trusting systems to regulate that access effectively.

As developers, our role isn't just to implement these systems. We must ensure they adapt, scale, and remain resilient regarding evolving challenges.

When your application grows, always prioritize revisiting and refining your authorization strategies. The digital realm is fluid, with emerging technologies and changing user behaviors. So, stay proactive, and informed. Always put security first, and you will grant a safer and smoother experience for all your users.

Always remember these two words in the web security and access control worlds: vigilance and evolution.