Welcome to the third lesson of the "Multi-Factor Authentication (MFA) in Express" course! In this lesson, we will focus on integrating MFA into an Express application. Building on the foundational concepts from the previous lesson, we will explore the practical steps necessary to enhance the security of your application by implementing MFA. Let's dive in and see how we can secure our application with MFA! 🚀

Now that you're familiar with the core MFA functions like generateSecret, verifyToken, verifyCode, and generateBackupCodes, let's focus on integrating these functions securely into your Express application. Proper integration is crucial - even with well-implemented MFA functions, vulnerabilities can arise from insecure application design. We'll examine how to store MFA data securely, protect sensitive endpoints, and create a robust authentication flow.

Security Reminder:

• Always encrypt MFA secrets at rest to prevent attackers from accessing them if your database is compromised.
• Always hash backup codes before storing them, just like passwords, so they cannot be used if leaked.
• Implement rate-limiting on all sensitive endpoints (such as /verify, /login, and /login/verify) to protect against brute-force attacks.

Let's examine a scenario where MFA is not properly integrated, leading to potential security vulnerabilities:

This code contains several critical vulnerabilities:

• No authentication checks - anyone can access this endpoint
• No validation that the user exists before accessing properties
• No protection against brute force attacks
• The endpoint updates user settings without proper authorization

To support MFA securely, we need to modify our user model to store MFA-related data, such as secrets and backup codes. This step is crucial for managing MFA settings for each user.

In this model, we store:

• mfaEnabled: Whether MFA is active for this user
• mfaSecret: The secret key for TOTP generation (should be encrypted at rest)
• backupCodes: JSON string of hashed backup codes for account recovery

Security Reminder:

• Never store MFA secrets or backup codes in plaintext.
• Use strong encryption for secrets and a secure hash function (e.g., bcrypt, Argon2) for backup codes.

Let's create a secure route for setting up MFA, using the functions you already know:

This secure implementation includes:

• Authentication middleware to ensure only logged-in users can access it
• Error handling for failed operations
• Proper user verification
• Temporary storage of the secret until verified
• Encryption of secrets and hashing of backup codes
• (In production) Add rate-limiting middleware to this endpoint

Next, we'll create a secure route to verify the MFA token provided by the user:

This implementation includes:

• Input validation for the token
• Authentication checks
• Verification that MFA is set up
• Proper error handling
• Session regeneration after successful verification
• Decryption of secrets before use
• (In production) Add rate-limiting middleware to this endpoint

When MFA is enabled, the login process becomes a two-step procedure. In this flow, a temporary token (often called a tempToken) is issued after the user successfully enters their username and password, but before they complete MFA verification.

A tempToken is a short-lived, signed token (such as a JWT or a random string stored server-side) that securely encodes the user's identity and the fact that they have passed the first authentication step. It is used to track the login session between the password and MFA steps, ensuring that only the correct user can proceed to MFA verification. Typically, a tempToken should expire quickly—commonly within 5 to 10 minutes—to minimize the risk of misuse.

In this lesson, we explored the secure integration of Multi-Factor Authentication into an Express application. We examined potential vulnerabilities, modified the user model, and created secure routes for setting up and verifying MFA. These integration patterns prevent common security issues while providing a solid user experience. As you move on to the practice exercises, you'll have the opportunity to implement these features and reinforce your understanding. In the next lessons, we'll continue to build on these concepts, further strengthening your application's security. Keep up the great work! 🌟