SvelteKit + Passkeys

Passkeys offer significant security and usability enhancements over passwords. We can use passkeys in isolation or as a secondary authentication factor. Whilst the technology behind passkeys is complex, frameworks and libraries such as Passlock make adoption simple.

This tutorial will take less than 30 mins to complete.

pnpm create @passlock/sveltekit

That’s it! check out the generated source code, which has plenty of comments.

If you like it, please give it a star 🙏

Alternatively, read on to learn how to do this manually…

Create a SvelteKit app

Use SvelteKit’s CLI to generate a skeleton project:

pnpm create svelte@latest my-app

Add the library

We’ll use Passlock’s SvelteKit library for passkey registration and authentication:

pnpm add -D @passlock/sveltekit

Create a registration route

Create a new template at src/routes/register/+page.svelte:

<!-- src/routes/register/+page.svelte -->
<form method="post">
  Email:
  <input type="text" name="email" />
  <br />

  First name:
  <input type="text" name="givenName" />
  <br />

  Last name:
  <input type="text" name="familyName" />
  <br />

  <button type="submit">Register</button>
</form>

This won’t win any design awards but I want to keep things real simple. Now for the real work … we’ll intercept the form submission and register a passkey on the users device:

<!-- src/routes/register/+page.svelte -->
<script lang="ts">
  import { enhance } from '$app/forms'
  import { register } from '@passlock/sveltekit'

  // we'll fill in the tenancyId and clientId later
  const { onSubmit } = register({ tenancyId: 'TBC', clientId: 'TBC' })
</script>

<form method="post" use:enhance={onSubmit}>
  Email:
  <input type="text" name="email" />
  <br />

  First name:
  <input type="text" name="givenName" />
  <br />

  Last name:
  <input type="text" name="familyName" />
  <br />

  <button type="submit">Register</button>
</form>

Explanation

We’re using SvelteKit’s progressive enhancement to intercept the form submission. We use Passlock’s SvelteKit extension to register a passkey on the user’s device. Passlock will store the public key component of the passkey in your Passlock vault.

If all goes well, this will return a token that we can exchange for a user object in our form action.

Process the token in the form action

The form will be submitted with an additional token field. We’ll use it to fetch the passkey details in the form action.

Create a new form action at src/routes/register/+page.server.ts:

// src/routes/register/+page.server.ts
import type { Actions } from './$types'
import { Passlock, TokenVerifier } from '@passlock/sveltekit'

// we'll replace the TBCs later
const tokenVerifier = new TokenVerifier({
  tenancyId: 'TBC',
  apiKey: 'TBC'
})

export const actions: Actions = {
  default: async ({ request }) => {
    const formData = await request.formData()
    const token = formData.get('token') as string
    const result = await tokenVerifier.exchangeToken(token)

    if (Passlock.isPrincipal(result)) {
      console.log(result)
    } else {
      console.error(result.message)
    }
  }
}

The result includes a sub field (subject / user id), along with an authId (authenticator i.e. passkey id). Later we’ll use these to link the passkey registration to a local user.

Create a Passlock account

We’ve used TBC for some Passlock config values. It’s time to replace these with real values.

Create a developer account at passlock.dev then head to the settings tab within your console. We’re after the tenancyId, clientId and apiKey values.

Edit your .env file (or .env.local) and create entries for these values:

# .env
PUBLIC_PASSLOCK_TENANCY_ID = '...'
PUBLIC_PASSLOCK_CLIENT_ID = '...'
PASSLOCK_API_KEY = '...'

If you don’t have a .env file in your application root, create one.

You can now reference these environment variables in your template and form actions:

<!-- src/routes/register/+page.svelte -->
<script lang="ts">
  import {
    PUBLIC_PASSLOCK_TENANCY_ID,
    PUBLIC_PASSLOCK_CLIENT_ID
  } from '$env/static/public'

  const { onSubmit } = register({ 
    tenancyId: PUBLIC_PASSLOCK_TENANCY_ID, 
    clientId: PUBLIC_PASSLOCK_CLIENT_ID, 
  })

  ...
</script>

// src/routes/register/+page.server.ts
import { PUBLIC_PASSLOCK_TENANCY_ID } from '$env/static/public'
import { PASSLOCK_API_KEY } from '$env/static/private'

const tokenVerifier = new TokenVerifier({
  tenancyId: PUBLIC_PASSLOCK_TENANCY_ID,
  apiKey: PASSLOCK_API_KEY
})

...

Try registering a passkey

Although we’re not yet finished, you should be at a point where you can register a passkey.

Navigate to the /register page and complete the form. You should be prompted to create a passkey and the form action will spit out details of the passkey registration.

You should also see an entry in the users tab of your Passlock console. The console can be used to view security related events, suspend and delete users and more.

Create a login route

We can now register a passkey on the users device. Let’s use that passkey to authenticate. The process is essentially the same as it was for registration.

Create a login template at src/routes/login/+page.svelte:

<!-- src/routes/login/+page.svelte -->
<script lang="ts">
  import { enhance } from '$app/forms'
  import { login } from '@passlock/sveltekit'

  import {
    PUBLIC_PASSLOCK_TENANCY_ID,
    PUBLIC_PASSLOCK_CLIENT_ID
  } from '$env/static/public'

  const { onSubmit } = login({ 
    tenancyId: PUBLIC_PASSLOCK_TENANCY_ID, 
    clientId: PUBLIC_PASSLOCK_CLIENT_ID
  })
</script>

<form method="post" use:enhance={onSubmit}>
  Email:
  <input type="text" name="email" />
  <br />

  <button type="submit">Login</button>
</form>

Notice how we’re only passing the email this time. Now for the form action:

// src/routes/login/+page.server.ts
import type { Actions } from './$types'
import { Passlock, TokenVerifier } from '@passlock/sveltekit'
import { PUBLIC_PASSLOCK_TENANCY_ID } from '$env/static/public'
import { PASSLOCK_API_KEY } from '$env/static/private'

const tokenVerifier = new TokenVerifier({
  tenancyId: PUBLIC_PASSLOCK_TENANCY_ID,
  apiKey: PASSLOCK_API_KEY
})

export const actions: Actions = {
  default: async ({ request }) => {
    const formData = await request.formData()
    const token = formData.get('token') as string
    const result = await tokenVerifier.exchangeToken(token)

    if (Passlock.isPrincipal(result)) {
      console.log(result)
    } else {
      console.error(result.message)
    }
  }
}

The form action is the same (at this stage). Passlock abstracts passkey registration and authentication into a common structure known as a Principal.

Try logging in with a passkey

Navigate to the /login page, enter your email (the one you used for registration) and click login. If all goes well, you should see your user details in the server console.

Within your Passlock console, under the users tab you should see an entry. If you click on the user you’ll be able to see the passkey registration and authentication events.

Summary

We used the Passlock library to register a passkey on the users device. The public key component of the passkey is stored in your Passlock vault.

During authentication we ask the user to present their passkey. Passlock verifies that the passkey is authentic, then generates a secure token. This token is passed to the backend form action in the form submission.

The form action verifies the secure token is authentic, exchanging it for details about the user and the passkey they used to authenticate.

Next steps

We’ve made a great start but we now need to link the passkeys to local user accounts and sessions. It’s time to use Lucia auth with passkeys