Passkeys promise a future where you never have to remember a password again and where phishing emails and credential stuffing attacks stop working.

If you're building or scaling a product, they reduce risk, lower support load, and ship a sign-in experience that doesn't feel like a tax on conversion. This article unpacks what passkeys are, why they're more secure than traditional authentication methods, and how they fit into today's browser and device ecosystem.

We'll then walk through a concrete Next.js implementation, focusing on both the registration flow (creating a passkey) and the authentication flow (signing in with it). You'll see how the browser, authenticator, and server coordinate using WebAuthn challenges, and how to wire it into a practical, end-to-end passkey experience.

TL;DR

• Passkeys replace passwords with public-key cryptography: the device generates a key pair, keeps the private key locked behind biometrics or a PIN, and the server stores only the public key.
• During sign-in, the server issues a one-time challenge that the device signs, proving possession without transmitting secrets.
• Passkeys are phishing-resistant (private key only responds to the original domain) and remove reusable credentials from your database.
• In Next.js, you can implement passkeys manually using the SimpleWebAuthn library with two round-trips each for registration and authentication.
• Or skip the complexity: Clerk supports passkeys with a single dashboard toggle and one component.

What are passkeys?

Passkeys are a modern, phishing-resistant form of passwordless authentication that replaces traditional passwords with cryptographic credentials tied to a user's device and unlocked locally via biometric authentication (for example, Face ID, Touch ID, or Windows Hello) or a device PIN. When a user registers, the device generates a public/private key pair. The server stores only the public key and challenges the device to prove possession of the private key during sign-in, so the private key never leaves the device. Passkeys provide multi-factor assurance because they combine something-you-have (the device) with something-you-are or something-you-know (biometric or PIN that unlocks the key), and they reduce server-side risk since attackers have no reusable secrets to steal.

Key benefits of passkey authentication

• Passwordless authentication: No passwords to create, remember, or leak.
• MFA built in by default: Device possession + local biometric or PIN unlock (or security key).
• Phishing-resistant: Private keys only sign challenges for the registering origin.
• Reduced server liability: Servers store only public keys, not reusable secrets.
• Simpler user experience: Faster sign-in flows and fewer account recovery calls.
• Cross-device sync: Platforms often let users sync passkeys between their devices for seamless access (implementation and privacy depend on the vendor).
• Attestation & device validation: Attestation is cryptographic proof that an authenticator provides about its identity and security properties (e.g., make, model, certification level). This optional feature helps servers verify authenticator properties during registration.
• Interoperability: Major browsers and platforms support passkeys via WebAuthn and CTAP standards.

Implementing passkeys in Next.js with WebAuthn

Building a complete passkeys implementation in Next.js from scratch would require many steps. Instead, we'll dive into a pre-built implementation and cover the important parts of the application as they pertain to passkeys to provide a clear understanding of how they work. The goal is to give you enough detail to evaluate effort and risk for your team, not to turn you into a security engineer.

The code for this article is available on GitHub. Feel free to review it in your browser or clone the repo to your machine to explore it. We'll cover the code in two sections:

• Registration will explain how a new user gets signed up with an application using a passkey.
• Authentication explains how a returning user signs in with their passkey.

This guide assumes familiarity with Next.js App Router, basic TypeScript, and a database for storing user credentials. The demo uses Postgres, but any database works.

Passkey registration flow

Before looking at the code, let's cover the workflow at a high level. The following diagram visually shows how areas of the application communicate with each other. Additional details for each step of the flow can be found below the image.

1. User enters username - The user types a username (and other data required for sign-up) into the registration form in the browser.
2. Browser requests registration options - The browser sends a request to the server asking for WebAuthn registration options for this user.
3. Server prepares options - The server creates the user record, generates a fresh random challenge, configures passkey settings, and returns the registration options to the browser.
4. Browser shows native registration prompt - The browser or OS shows a built-in prompt such as "Create a passkey" or "Use Face ID to register".
5. User approves with biometrics or a security key - The user completes the biometric check or interacts with their security key so the authenticator can proceed.
6. Authenticator creates a new key pair - The authenticator creates a new public/private key pair for this site. The private key stays on the device and is never sent to the server.
7. Browser sends credential to the server - The browser sends the new credential data (including the public key and associated identifiers) back to the server.
8. Server validates and stores the credential - The server validates the challenge and signature, then stores the credential ID, public key, and metadata so this passkey can be used for future logins.
9. Registration completes - The server responds with success, and the browser updates the UI to indicate that passkey registration is complete.

The client-side registration component

Now that you understand how the workflow operates, let's dive into the code, starting with the PasskeyRegister component. The demo application mounts this component on the homepage and allows the user to enter their desired username and a display name. When the user submits the form, the component first checks the current browser for WebAuthn support, then sends the data to the /api/register/options endpoint.

The code uses the SimpleWebAuthn library to handle the WebAuthn protocol details:

Generating passkey registration options on the server

When the server receives the form data, it creates the user record in the database. Using the @simplewebauthn/server package, the server creates a series of options and stores a cryptographic challenge in the database. This challenge is a high-entropy, single-use string that the next step of the process uses.

These options define the relying party and user identity, configure how the authenticator should behave (for example, preferring passkey-style resident credentials and user verification), and use the timeout and generated challenge to control how long and under what conditions the client (typically the user's browser) will allow the registration to continue.

The server returns the object created from the options to the client along with the challenge.

The client receives the challenge and generates a public/private key pair. The private key is stored on the device that created it and never leaves that device. It is used to digitally sign the challenge that was received from the server. The client also creates a "credential ID," which uniquely identifies that device and is stored in the database, enabling a single account to register multiple passkeys if needed.

Once complete, the client sends the signed challenge, public key, and credential ID back to the server. The startRegistration function provided by @simplewebauthn/browser triggers this second trip to the server (shown in the client-side code above).

Verifying the passkey registration response

When the server receives this payload, it retrieves the user and challenge from the database. Using the provided public key, the server verifies the signature and (assuming the verification succeeds) stores that public key as a passkey for the user.

Once this process completes, the server deletes the challenge from the database. Since each challenge has an expiration time (60 seconds in this demo), the entire flow must complete within the specified time; otherwise, it becomes invalid.

Passkey authentication flow

Authenticating with passkeys follows a similar flow to registration. While the details of each step are different, the number of steps involved in authentication is the same:

1. User enters username - The user types their username into the sign-in form in the browser.
2. Browser requests authentication options - The browser sends a request to the server asking for WebAuthn options (including a fresh challenge) for this username.
3. Server prepares options - The server looks up the user, finds their registered passkeys, generates a new random challenge, and sends the authentication options back to the browser.
4. Browser shows native authentication prompt - The browser or OS shows a built-in prompt such as "Sign in with Face ID?" or "Use your security key".
5. User approves with a passkey - The user completes the biometric check or uses their security key. The authenticator unlocks the private key stored on the device.
6. Authenticator signs the challenge - The authenticator signs the challenge (and related data) with the private key. The private key never leaves the device.
7. Browser sends the signed result to the server - The browser sends the credential data (including the signature and identifiers) to the server for verification.
8. Server verifies the response - The server looks up the matching public key, checks that the challenge is valid and unused, and verifies the signature and counter.
9. User is signed in - If everything checks out, the server responds with success and the browser updates the UI to show that the user is signed in (and typically establishes a session or issues a token).

The client-side authentication component

In the PasskeyAuth component, the user enters their username and submits the form. The component sends this data to the /api/auth/options endpoint.

Generating passkey authentication options on the server

On the server, the user is retrieved from the database along with their registered passkeys. The server creates authentication options using details for each of the user's credentials (allowing the use of any passkeys the user owns), and stores the challenge in the database before sending the options back to the client.

Verifying the passkey authentication response

Assuming the client has access to one of the registered passkeys, the private key associated with that passkey signs the challenge and sends the signature back to the server for verification. As with registration, @simplewebauthn/browser handles the second trip back to the server, this time with the startAuthentication method. Once the client signs the challenge, it sends the signed challenge to the /api/auth/verify endpoint for verification.

A verified signature indicates the user is authenticated. At this point, you'd typically create a session and set a cookie or return a JWT.

Clerk makes passkeys simple

Clerk supports passkeys out of the box with a simple toggle in our dashboard:

Once enabled, any mounted <SignIn /> or <SignUp /> components will present your users with an option to register or authenticate using passkeys, supporting the workflows described above without building, testing, or maintaining code.

All it takes is a single line of code in your project to render this form:

For growth-minded engineering teams, this is a build‑vs‑buy decision: do you want engineers investing cycles in auth primitives, or in features that move activation, retention, and revenue?

Beyond passwordless: Complete User Management

Furthermore, our platform offers more than sign-up and sign-in using passkeys. You can enable additional authentication options your users expect (email codes, social sign in, etc.), and you don't have to own the edge cases around recovery, device changes, and evolving platform behavior.

On top of authentication, you get an easy way for your users to self-serve their needs, from user profile details to password resets. For B2B apps, you can use Organizations to enable multi-tenancy support for your application in a few lines of code, while supporting passkeys across all tenants of your application, a requirement that often shows up in enterprise evaluations sooner than founders expect.

Conclusion

Passkeys remove much of the pain and risk of authentication by replacing brittle passwords with strong, origin-bound cryptography. By leaning on platform authenticators and standards like WebAuthn and FIDO2, you get phishing resistance and built-in MFA without making users jump through extra hoops, and you reduce the blast radius of credential theft for your company.

In this tutorial, we explored what passkeys are, how the registration and authentication flows work, and how to wire them up end-to-end in a Next.js app using SimpleWebAuthn. We also explored how simple it is to add passkeys to your application with Clerk, while reducing effort around testing and maintenance. To get started with Clerk, check out our quickstart guide or learn more about passkey configuration options.