Chrome Extension Patterns

CRITICAL RULES

1. OAuth (Google, GitHub, etc.) and SAML are NOT supported in popups or side panels -- use syncHost to delegate auth to your web app
2. Email links (magic links) don't work in popups -- the popup closes when the user clicks outside, resetting sign-in state
3. Side panels don't auto-refresh auth state -- users must close and reopen the side panel after signing in via the web app
4. Service workers and content scripts have NO access to Clerk React hooks -- use createClerkClient() or message passing
5. Extension URLs use chrome-extension:// not http:// -- all redirect URLs must use chrome.runtime.getURL('.')
6. Without a stable CRX ID, every rebuild breaks auth -- configure key in manifest BEFORE deploying
7. Content scripts cannot use Clerk directly due to origin restrictions -- Clerk enforces strict allowed origins
8. Bot protection must be DISABLED in Clerk Dashboard -- Cloudflare bot detection is not supported in extension environments

Authentication Options

Method	Popup	Side Panel	syncHost (with web app)
Email + OTP	Yes	Yes	Yes
Email + Link	No	No	Yes
Email + Password	Yes	Yes	Yes
Username + Password	Yes	Yes	Yes
SMS + OTP	Yes	Yes	Yes
OAuth (Google, GitHub, etc.)	NO	NO	YES
SAML	NO	NO	YES
Passkeys	Yes	Yes	Yes
Google One Tap	No	No	Yes
Web3	No	No	Yes

Quick Start (Plasmo)

npx create-plasmo --with-tailwindcss --with-src my-extension
cd my-extension
npm install @clerk/chrome-extension

Enable Native API in Clerk Dashboard under Native applications. Required for all extension integrations.

.env.development:

PLASMO_PUBLIC_CLERK_PUBLISHABLE_KEY=pk_test_...
CLERK_FRONTEND_API=https://your-app.clerk.accounts.dev

src/popup.tsx:

import { ClerkProvider, Show, SignInButton, SignUpButton, UserButton } from '@clerk/chrome-extension'

const PUBLISHABLE_KEY = process.env.PLASMO_PUBLIC_CLERK_PUBLISHABLE_KEY
const EXTENSION_URL = chrome.runtime.getURL('.')

if (!PUBLISHABLE_KEY) {
  throw new Error('Missing PLASMO_PUBLIC_CLERK_PUBLISHABLE_KEY')
}

function IndexPopup() {
  return (
    <ClerkProvider
      publishableKey={PUBLISHABLE_KEY}
      afterSignOutUrl={`${EXTENSION_URL}/popup.html`}
      signInFallbackRedirectUrl={`${EXTENSION_URL}/popup.html`}
      signUpFallbackRedirectUrl={`${EXTENSION_URL}/popup.html`}
    >
      <Show when="signed-out">
        <SignInButton mode="modal" />
        <SignUpButton mode="modal" />
      </Show>
      <Show when="signed-in">
        <UserButton />
      </Show>
    </ClerkProvider>
  )
}

export default IndexPopup

Use mode="modal" for SignInButton -- navigating to a separate page breaks the popup flow.

syncHost -- Sync Auth with Web App

Use this when you need OAuth, SAML, or want the extension to reflect sign-in from your web app.

How it works: The extension reads the Clerk session cookie from your web app's domain via host_permissions.

Step 1 -- Environment variables:

.env.development:

PLASMO_PUBLIC_CLERK_PUBLISHABLE_KEY=pk_test_...
CLERK_FRONTEND_API=https://your-app.clerk.accounts.dev
PLASMO_PUBLIC_CLERK_SYNC_HOST=http://localhost

.env.production:

PLASMO_PUBLIC_CLERK_PUBLISHABLE_KEY=pk_live_...
CLERK_FRONTEND_API=https://clerk.your-domain.com
PLASMO_PUBLIC_CLERK_SYNC_HOST=https://clerk.your-domain.com

Step 2 -- Add syncHost prop:

const SYNC_HOST = process.env.PLASMO_PUBLIC_CLERK_SYNC_HOST

<ClerkProvider
  publishableKey={PUBLISHABLE_KEY}
  syncHost={SYNC_HOST}
  afterSignOutUrl="/"
  routerPush={(to) => navigate(to)}
  routerReplace={(to) => navigate(to, { replace: true })}
>

Step 3 -- Configure host_permissions in package.json:

{
  "manifest": {
    "key": "$CRX_PUBLIC_KEY",
    "permissions": ["cookies", "storage"],
    "host_permissions": [
      "$PLASMO_PUBLIC_CLERK_SYNC_HOST/*",
      "$CLERK_FRONTEND_API/*"
    ]
  }
}

Step 4 -- Add extension ID to web app's allowed origins via Clerk API:

curl -X PATCH https://api.clerk.com/v1/instance \
  -H "Authorization: Bearer YOUR_SECRET_KEY" \
  -H "Content-type: application/json" \
  -d '{"allowed_origins": ["chrome-extension://YOUR_EXTENSION_ID"]}'

Hide unsupported auth methods in popup when using syncHost:

<SignIn
  appearance={{
    elements: {
      socialButtonsRoot: 'plasmo-hidden',
      dividerRow: 'plasmo-hidden',
    },
  }}
/>

Full guide: references/sync-host.md

createClerkClient() for Vanilla JS / Service Workers

Import from @clerk/chrome-extension/client (not @clerk/chrome-extension).

Background service worker (src/background/index.ts):

import { createClerkClient } from '@clerk/chrome-extension/client'

const publishableKey = process.env.PLASMO_PUBLIC_CLERK_PUBLISHABLE_KEY

async function getToken(): Promise<string | null> {
  const clerk = await createClerkClient({
    publishableKey,
    background: true,
  })
  if (!clerk.session) return null
  return await clerk.session.getToken()
}

chrome.runtime.onMessage.addListener((request, sender, sendResponse) => {
  getToken()
    .then((token) => sendResponse({ token }))
    .catch((error) => {
      console.error('[Background] Error:', JSON.stringify(error))
      sendResponse({ token: null })
    })
  return true
})

The background: true flag keeps sessions fresh even when popup/sidepanel is closed. Without it, tokens expire after 60 seconds.

Popup with vanilla JS (src/popup.ts):

import { createClerkClient } from '@clerk/chrome-extension/client'

const EXTENSION_URL = chrome.runtime.getURL('.')
const POPUP_URL = `${EXTENSION_URL}popup.html`

const clerk = createClerkClient({ publishableKey })

clerk.load({
  afterSignOutUrl: POPUP_URL,
  signInForceRedirectUrl: POPUP_URL,
  signUpForceRedirectUrl: POPUP_URL,
  allowedRedirectProtocols: ['chrome-extension:'],
}).then(() => {
  clerk.addListener(render)
  render()
})

Full guide: references/create-clerk-client.md

Headless Extension (no popup, no side panel)

For extensions that run entirely in the background and sync with a web app.

Uses syncHost + createClerkClient with background: true to read auth state from the web app's cookies.

import { createClerkClient } from '@clerk/chrome-extension/client'

const publishableKey = process.env.PLASMO_PUBLIC_CLERK_PUBLISHABLE_KEY
const syncHost = process.env.PLASMO_PUBLIC_CLERK_SYNC_HOST

async function getAuthenticatedUser() {
  const clerk = await createClerkClient({
    publishableKey,
    syncHost,
    background: true,
  })
  return clerk.user
}

Requires host_permissions for the sync host domain in package.json.

Full guide: references/headless-extension.md

Content Scripts

Content scripts run in an isolated JavaScript world injected into web pages. Clerk cannot be used directly -- origin restrictions prevent it.

Use message passing to request auth state from the background service worker:

// content.ts
async function getToken(): Promise<string | null> {
  return new Promise((resolve) => {
    chrome.runtime.sendMessage({ type: 'GET_TOKEN' }, (response) => {
      resolve(response?.token ?? null)
    })
  })
}

async function main() {
  const token = await getToken()
  if (!token) return
  // use token for authenticated API calls
}

main()

Full guide: references/content-scripts.md

Stable CRX ID

Without a pinned key, Chrome derives the CRX ID from a random key at build time. This rotates every rebuild, breaking allowed origins.

Option A -- Plasmo Itero (recommended):

1. Visit Plasmo Itero Generate Keypairs
2. Click "Generate KeyPairs" -- save Private Key securely, copy Public Key and CRX ID

Option B -- OpenSSL:

openssl genrsa -out key.pem 2048
# Use Plasmo Itero to convert or extract the public key in correct format

.env.chrome:

CRX_PUBLIC_KEY="<PUBLIC KEY from Itero>"

package.json:

{
  "manifest": {
    "key": "$CRX_PUBLIC_KEY",
    "permissions": ["cookies", "storage"],
    "host_permissions": [
      "http://localhost/*",
      "$CLERK_FRONTEND_API/*"
    ]
  }
}

Add chrome-extension://YOUR_STABLE_CRX_ID to Clerk Dashboard > Allowed Origins.

Token Cache (persist across popup closes)

const tokenCache = {
  async getToken(key: string) {
    const result = await chrome.storage.local.get(key)
    return result[key] ?? null
  },
  async saveToken(key: string, token: string) {
    await chrome.storage.local.set({ [key]: token })
  },
  async clearToken(key: string) {
    await chrome.storage.local.remove(key)
  },
}

<ClerkProvider publishableKey={PUBLISHABLE_KEY} tokenCache={tokenCache}>

Storage type	Scope	Clears on
chrome.storage.local	Device	Uninstall or manual clear
chrome.storage.session	Session	Browser close
chrome.storage.sync	All devices	Uninstall (size-limited, 8KB)
localStorage	Popup only	Popup close -- do not use for auth

Common Pitfalls

Symptom	Cause	Fix
Redirect loop on sign-in	Missing CRX URL in ClerkProvider props	Set afterSignOutUrl, signInFallbackRedirectUrl
OAuth button not working	OAuth not supported in popup	Use syncHost to delegate to web app
Auth state stale after web app sign-in	syncHost not configured	Add syncHost prop + host_permissions
Side panel shows signed-out after web sign-in	Known limitation	User must close and reopen the side panel
Background can't get token after 60s	Session expired, no background refresh	Use createClerkClient({ background: true })
Content script can't access Clerk	Isolated world + origin restrictions	Use message passing to background service worker
Auth breaks after rebuild	CRX ID rotated	Configure stable key via .env.chrome
PLASMO_PUBLIC_ var undefined	Wrong env file	Use .env.development, not .env
Bot protection errors	Cloudflare not supported in extensions	Disable bot protection in Clerk Dashboard
Token cache not persisting	Using localStorage in popup	Use chrome.storage.local or pass tokenCache prop

Plan Requirements

Feature	Plan
Basic popup auth (email/password, OTP)	Free
Passkeys	Free
syncHost	Requires Pro (custom domain)
OAuth through syncHost	Pro + OAuth configured on web app
SAML through syncHost	Enterprise
Bot protection	N/A -- must be disabled for extensions

See Also

• clerk-setup - Initial Clerk install
• clerk-custom-ui - Custom flows & appearance