Two-Factor Authentication (2FA): Strengthen Your App Security

Whether you're building a banking app, an e-commerce platform, or an internal business tool, adding an extra layer of authentication can dramatically improve security without creating unnecessary friction for users.

If you’d like to know why it’s imperative that you provide your service users with two-factor authentication and how to implement it faster and more cost-efficiently without the need for custom integrations, read on.

Key Takeaways:

• 2FA significantly reduces the risk of unauthorized access, even if a password is compromised.
• Authentication factors fall into three categories: something you know, something you have, or something you are.
• Authenticator apps, Passkeys, biometrics, and security keys are generally more secure than SMS verification.
• 2FA helps defend against phishing and many common social engineering attacks.
• Email, banking, cloud storage, and business accounts should always use 2FA.
• Passkeys are shaping the future of authentication by combining security and convenience.
• Production-ready authentication solutions can help teams implement 2FA faster and more reliably.

What is Multi-Factor Authentication (MFA)?

First, let’s start with some definitions.

We can define multi-factor authentication as a security mechanism that requires two or more distinct forms of identification to verify a user's identity before granting access to an account or system. This adds an extra layer of protection compared to relying solely on a password. Consequently, Two-Factor Authentication is a mechanism that requires two forms of identification.

In simple terms, when your user logs into your service, they will be asked to verify their identity twice, using different user authentication methods, which I will explore later in the coming chapters.

With the rise in cybercrime and data breaches, 2FA is crucial for protecting sensitive information and preventing unauthorized access to online accounts.

Two-factor authentication is just one part of a secure authentication strategy. Check out our article Authentication & Registration Best Practices: From Sign-Up to Account Recovery.

Types of 2FA

Now that we know what 2FA is, let us take a closer look at what the word ‘factor’ actually stands for and what it means in practice to use ‘two factors of authentication’.

Authentication factors

There are three distinct factors that your users can use to authenticate themselves when requesting access.

• Something you know: This includes information only the user should know, such as a password, PIN, or answers to security questions. 
• While, in theory, it’s impossible to get into your user’s head and steal information, that’s not really how it plays out in practice. Bad actors can use social engineering to get that info from them, sometimes without them even noticing.
• On top of that, poor security practices can lead to issues with this factor, such as leaving the PIN on a sticky note attached to the laptop.
• Something you have: a physical object in your user’s possession, such as a smartphone, a security key, or a hardware token. 
• The strength of handling authentication requests with something that’s in one’s physical possession is that your users are much safer against bad actors at any distance. For instance, a group of hackers from a different country can’t get hold of the device.
• However, it is vulnerable to the very simple act of stealing the physical device – although, in most cases, one wouldn’t be able to easily unlock it to actually use it.
• Something you are: This utilizes your users’ unique biological traits for verification, such as fingerprints, facial recognition, or iris scans. 
• Biometrics offer a high level of security as they are very difficult to replicate.
• While very secure, there are concerns that something might happen and the user might be unable to use that method; for instance, their hand might be burnt, they might alter their fingerprint, or their face might be disfigured in an accident.

2FA, therefore, is a combination of two of the three available factors to diversify our lines of defense against a potential bad actor. While each of them has its own weaknesses and attack vectors, it takes significantly more effort to circumvent these security measures when multiple factors are in place.

Second factor methods – examples

There are numerous examples of 2FA methods that illustrate the idea and how it looks in practice.

1. One-time passwords (OTP): These are temporary codes generated by an app or sent via SMS, valid for a single login attempt.

a) SMS delivery: While convenient, SMS messages can be intercepted, making this method less secure.

b) Authenticator apps (like Google Authenticator): These apps generate time-based one-time passwords (TOTP) that change every N seconds, providing a more secure alternative to SMS. These apps are tied to your specific device.

2. Push notifications: With this method, the user receives a notification on their phone prompting them to approve or deny a login attempt. This provides real-time verification and is generally considered secure.

3. Hardware tokens: Small physical devices that generate unique codes, often used in high-security environments. These offer strong security but can be lost or damaged.

4. Biometric verification: Using fingerprint, face, or other biological traits to verify identity. This method is convenient and increasingly common on smartphones and laptops.

5. Location-based authentication: This niche method uses location as an authentication factor. Systems can be set up to only allow logins from specific locations or to flag login attempts from unusual locations. This adds another layer of security by taking context into account.

How Two-Factor Authentication Works

Let me provide an analogy that visually illustrates how 2FA works, using a very common example: an ATM.

When you go to an ATM to withdraw cash, 2FA is built into it, even though it doesn’t jump out at you. ATMs require something you know (PIN) and something you have (a physical card). One couldn’t access your bank account without both – simply stealing the card is insufficient, and peeking at your PIN is insufficient too.

This highlights the core principle of 2FA – a single point of failure is eliminated, making your users’ accounts more resilient to attacks.

2FA and MFA in action: real-world examples

In addition to the ATM analogy we mentioned earlier, here are some more examples of practical 2FA applications.

• Online banking: Banks require MFA to log in and make transactions, often using OTPs or push notifications to verify your intention. That’s also layered on top of re-authentication, making it supremely secure.
• Social media: Platforms like Facebook and Twitter/X offer 2FA to protect accounts from unauthorized access, typically via authenticator apps or SMS codes.
• Email accounts: Enabling 2FA for your email is crucial, as this is where you regain access to other accounts and services. The user receives all recovery codes and confirmation messages here, so it’s imperative that it is protected from unwanted access.
• Admin access: If there’s an admin designated for a service, they will typically have a highly secure path to access the account, using multi-factor authentication.

How 2FA protects against social engineering

While we’re all afraid of genius hackers who can go through millions of combinations of passwords to get into your account, Social Engineering is arguably the scariest and most real threat one could encounter on a daily basis.

Here, by social engineering, we mean a type of psychological manipulation that aims to obtain key confidential information from the target, sometimes without the target noticing.

An example would be situations where your user is called by someone claiming to be the service admin or IT support, asking for their credentials to verify their identity, even though this is exactly when the ‘something you know’ factor is being compromised.

2FA helps protect against these threats by requiring a second factor that attackers are unlikely to have. Even if they trick the user into revealing their password, they still need the user’s phone or security key to gain access.

While 2FA isn't foolproof, it significantly reduces the risk of falling victim to social engineering attacks that exploit human vulnerabilities.

How to enable 2FA

It’s very likely that after reading the piece, you can go to the services you already use and immediately enable 2FA. It’s such a well-respected industry standard that most applications will offer that option.

Enabling 2FA typically involves navigating to your account's security settings, choosing a 2FA method, and following the provided instructions. It might involve scanning a QR code with an authenticator app or setting up Face ID. The best place to start is your email, where many other authentication codes and magic links get sent when you forget your password or otherwise wish to regain access to an account.

Services tend to urge users to enable 2FA even if they haven’t done so themselves. It’s typically in the form of CTAs (call-to-action), like a banner at the top of the screen. While snoozing such reminders is easy, adhering to these guidelines and enabling 2FA is highly recommended from a security perspective.

Industry examples of 2FA

As I’ve mentioned before, two-factor authentication methods are a security industry standard. The biggest tech leaders on the market have used them for a long time and continue to innovate to maintain the highest security standards.

Below, you will find some examples from companies you’ve definitely heard of.

Passkeys and the future of 2FA

In the cybersecurity world, there’s an authentication method called PassKeys.

In short, Passkeys are a passwordless method of authentication that uses public-key cryptography and are closely tied to the inner workings of the physical device you use. It uses biometrics or the device’s PIN to verify your identity. They inherently combine two factors – the device (what you have) and biometrics (who you are) or a PIN (what you know). In a way, one could say this is a single method with 2FA baked in. If you use Passkeys as your default login method, you're pre-equipped with the security measures discussed previously.

However, Passkeys can also be used as a factor in the authentication process, whether as the first or second factor. Typically, though, you’ll see passkeys as the first line of defense, with a password as the second step – but used for high-security environments like admin access.

Passkeys are becoming one of the most promising alternatives to traditional passwords and even simplify many 2FA scenarios. If you'd like to understand how they work, their security benefits, and when to use them, read “Passkeys Explained: How Passwordless Authentication Works.”

Losing your 2FA device

If your user has tied their 2FA factor to a specific device, such as a phone with an authenticator app, losing that device might be pretty problematic. Thankfully, this particular issue can be mitigated easily if approached correctly.

First, one can set up the authenticator app on multiple devices, such as a phone and a tablet. If the user doesn't tend to carry both, they don’t risk a situation where stealing their backpack would leave them without access to both. This can be a way to prevent issues linked to losing access to a single user’s device.

On top of that, numerous services provide recovery codes with their 2FAs. These are typically codes that one ought to store somewhere safe, preferably offline, where nobody can access them.

Furthermore, users can use alternative authentication methods as a fallback if they lose the device. This can include a security question or email.

As a last resort, users should also be able to contact customer support directly, which, albeit slowly, should resolve the issue with minimal effort.

Pros and cons of 2FA

With a full understanding of what 2FA is and how it works, let’s now carefully consider the upsides and also the downsides of this security measure.

Pros

• Strengthened security access against bad actors: 2FA significantly reduces the risk of unauthorized access, even if a password is compromised, thanks to its immunity to single-point attacks.
• Enhanced user trust and confidence: Knowing that their accounts are protected by 2FA increases users' trust in your online service.
• Compliance with security standards: Many industries and regulations require 2FA to protect sensitive data.

Cons

• Potential inconvenience: Adding an extra step to the login process can be slightly less convenient.
• There is a super user-friendly way to approach this topic if you value user experience highly, and that’s the aforementioned Passkeys, which provide a seamless flow with a high degree of security.
• Issues with lost mobile devices: Losing the 2FA device can make it difficult to access accounts.
• However, as mentioned previously, there are highly effective prevention and mitigation measures to address the issue.
• Vulnerabilities of certain methods: SMS-based 2FA can be vulnerable.
• Thankfully, there are great alternatives to 2FA, such as authenticator apps, that make it very safe.
• Integration and upfront implementation costs:
• If you opt for a custom integration, the initial cost might be quite high.
• However, there are options to reduce costs, including using proven, out-of-the-box solutions offered by some software development service providers.

When to use 2FA

When should one use 2FA, then? A very predictable but painfully honest answer would be to use it everywhere to make the user’s digital presence as secure as possible. However, we can prioritize some types of accounts over others to begin with.

2FA is essential for any account containing personal, financial, or confidential data.

• Financial accounts: Banks, online payment systems, investment platforms.
• Email accounts: Often the key to other accounts, they are a prime target.
• Social media accounts: Protecting personal information and one’s online reputation.
• Cloud storage services: Securing files and data stored in the cloud.
• Work accounts and business systems: Protecting company data and preventing unauthorized access.

Security is one of the essential features users expect from modern applications. Our 30 High-Impact Features in Mobile Apps checklist covers other capabilities worth considering before starting development. 

How to implement 2FA

If you’d like to implement 2FA in your service, there are two main routes to do so – which I’ve alluded to a couple of times throughout the piece.

• Custom integration
• This would require all the steps that you might expect, ranging from custom UI and accessibility to backend integration to testing and debugging.
• Using ready, out-of-the-box solutions
• This approach is much more time- and capital-efficient, as you can leverage pre-built, battle-tested templates. If you're building a Flutter application, our Flutter Mobile App Template includes production-ready authentication, authorization, and other core app features, making it much faster to add secure authentication flows such as 2FA.

Conclusions

Two-factor authentication has become one of the simplest and most effective ways to strengthen account security. While no authentication method is completely immune to attacks, adding a second verification factor dramatically reduces the likelihood of unauthorized access.

As authentication continues to evolve with technologies like Passkeys, implementing strong, user-friendly authentication is no longer just a security enhancement - it's an expectation. Whether you're building a new application or improving an existing one, investing in modern authentication will benefit both your users and your business.