Skip to main content
Docs
Dashboard

Configure Clerk Content-Security-Policy headers

Content-Security-Policy (CSP) headers secure your document by preventing resources from being loaded from unexpected sources. This protects your apps from XSS attacks and data injections.

For Clerk to work correctly in your application, the following CSP directives are required:

  1. script-src - This value should include the host application's FAPI hostname, such as https://clerk.your-domain.com, as well as cloudflare's bot protection host, https://challenges.cloudflare.com.
  2. connect-src - This value should include the host application's FAPI hostname, such as https://clerk.your-domain.com.
  3. img-src - This value should be https://img.clerk.com.
  4. worker-src - Use the 'self' value to indicate that workers can be loaded from first-party scripts. The blob: schema value also needs to be included.
  5. style-src - This value should include 'unsafe-inline' due to Clerk's usage of runtime CSS-in-JS for styling.
  6. frame-src - This value should include cloudflare's bot protection host, https://challenges.cloudflare.com.

There are two ways to configure your CSP headers:

  1. Automatic CSP configuration - This is available for the Next.js SDK only. Clerk provides built-in support for automatically injecting CSP headers through middleware. This simplifies the process of setting up a secure CSP that works correctly with Clerk.
  2. Manual CSP configuration

Automatic CSP configuration

Warning

Automatic CSP configuration is available only for @clerk/nextjs >=6.14.0.

Clerk provides built-in support for automatically injecting CSP headers by adding the contentSecurityPolicy option to your clerkMiddleware(). There are two modes available depending on how strict you want your CSP to be:

default configuration

The default configuration will apply the following CSP directives:

  • connect-src - 'self' https://clerk-telemetry.com https://*.clerk-telemetry.com https://api.stripe.com https://maps.googleapis.com https://{{fapi_url}}
  • default-src - 'self'
  • form-action - 'self'
  • frame-src - 'self' https://challenges.cloudflare.com https://*.js.stripe.com https://js.stripe.com https://hooks.stripe.com
  • img-src - 'self' https://img.clerk.com
  • script-src - 'self' 'unsafe-inline' https http https://*.js.stripe.com https://js.stripe.com https://maps.googleapis.com
  • style-src - 'self' 'unsafe-inline'
  • worker-src - 'self' blob:
middleware.ts
import { clerkMiddleware, createRouteMatcher } from '@clerk/nextjs/server'

const isPublicRoute = createRouteMatcher(['/sign-in(.*)', '/sign-up(.*)'])

export default clerkMiddleware(
  async (auth, request) => {
    if (!isPublicRoute(request)) {
      await auth.protect()
    }
  },
  {
    contentSecurityPolicy: {},
  },
)

strict configuration

When using the strict configuration, Clerk will:

  1. Automatically generate a unique nonce for each request.
  2. Configure the CSP header with appropriate directives.
  3. Make the nonce available to your application through the x-nonce header.

The middleware will handle passing the nonce to the <ClerkProvider> automatically, so you don't need to manually set the nonce prop when using server components.

middleware.ts
import { clerkMiddleware, createRouteMatcher } from '@clerk/nextjs/server'

const isPublicRoute = createRouteMatcher(['/sign-in(.*)', '/sign-up(.*)'])

export default clerkMiddleware(
  async (auth, request) => {
    if (!isPublicRoute(request)) {
      await auth.protect()
    }
  },
  {
    contentSecurityPolicy: {
      strict: true,
    },
  },
)

Important

You must pass the dynamic prop to <ClerkProvider> for strict CSP configuration to work correctly. This is because the nonce value is generated on the server and passed to the client, which requires dynamic rendering.

app/layout.tsx
import { ClerkProvider } from '@clerk/nextjs'

export default function Layout({ children }) {
  return (
    // When using clerkMiddleware with `strict` configuration,
    // the nonce is automatically provided.
    // No need to manually set the `nonce` prop on `<ClerkProvider>`
    <ClerkProvider dynamic>
      <html lang="en">
        <body>{children}</body>
      </html>
    </ClerkProvider>
  )
}

If you need to apply the nonce to custom scripts, you can access it through the headers:

pages/index.tsx
import { headers } from 'next/headers'

export default function Page() {
  const nonce = headers().get('x-nonce')

  return (
    <div>
      <script nonce={nonce} src="/custom-script.js" />
    </div>
  )
}

Add additional CSP directives

You can customize your Content Security Policy (CSP) by adding your own directives to either the default or strict configurations. Simply provide a directives object, and your custom rules will be merged with Clerk's default security settings.

In the following example, the connect-src directive is configured to include api.example.com and analytics.example.com, and the img-src directive is configured to include images.example.com.

middleware.ts
import { clerkMiddleware, createRouteMatcher } from '@clerk/nextjs/server'

const isPublicRoute = createRouteMatcher(['/sign-in(.*)', '/sign-up(.*)'])

export default clerkMiddleware(
  async (auth, request) => {
    if (!isPublicRoute(request)) {
      await auth.protect()
    }
  },
  {
    contentSecurityPolicy: {
      strict: true,
      directives: {
        'connect-src': ['api.example.com', 'analytics.example.com'],
        'img-src': ['images.example.com'],
      },
    },
  },
)

Manual CSP configuration

The following example demonstrates a Next.js config file that sets the necessary directives for your application's assets and Clerk to load and function correctly. The values used in the example are generated from your currently selected instance in the Clerk Dashboard. Make sure to handle both your development instance and production instance hosts.

Warning

You will need to make sure any third-party domains where scripts or assets are loaded from are also specified.

next.config.js
const cspHeader = `
  default-src 'self';
  script-src 'self' 'unsafe-inline' 'unsafe-eval' https://YOUR_FRONTEND_API_URL https://challenges.cloudflare.com;
  connect-src 'self' https://YOUR_FRONTEND_API_URL;
  img-src 'self' https://img.clerk.com;
  worker-src 'self' blob:;
  style-src 'self' 'unsafe-inline';
  frame-src 'self' https://challenges.cloudflare.com;
  form-action 'self';
`

/** @type {import('next').NextConfig} */
const nextConfig = {
  async headers() {
    return [
      {
        source: '/(.*)',
        headers: [
          {
            key: 'Content-Security-Policy',
            value: cspHeader.replace(/\n/g, ''),
          },
        ],
      },
    ]
  },
}

module.exports = nextConfig

Usage of unsafe-eval and unsafe-inline directives in Next.js

  • Within script-src, unsafe-eval is a requirement for Next.js to run in development mode. For production environment CSPs, it should be removed.
  • Within script-src, unsafe-inline is a requirement for Next.js in both dev and prod environments if you're using the App Router and not using strict-dynamic. If you are using the Pages Router, it can be removed.
  • Within style-src, unsafe-inline is a requirement for Clerk's components to inject their styles. Removing this requirement is on our roadmap. If you'd like to see this implemented sooner, contact support.

Implementing a strict-dynamic CSP

If you'd like to manually implement a strict-dynamic CSP, Clerk supports this, but with a different type of configuration. As strict-dynamic CSPs require a "nonce" value that should be programmatically generated per-request, the best way to make this work is within middleware that runs on every request. The following example demonstrates how to implement a strict-dynamic CSP with Next.js middleware, but the same approach could be used with any other framework.

Note

This is not necessary if you are using the strict-dynamic mode in clerkMiddleware(). This is only necessary if you are manually implementing a strict-dynamic CSP.

middleware.ts
import { NextResponse } from 'next/server'
import { clerkMiddleware } from '@clerk/nextjs/server'

export default clerkMiddleware((auth, req) => {
  return applyCsp(req)
})

function applyCsp(req) {
  // create a randomly generated nonce value
  const nonce = Buffer.from(crypto.randomUUID()).toString('base64')

  // format the CSP header
  const cspHeader = `
    default-src 'self';
    script-src 'self' 'strict-dynamic' 'nonce-${nonce}' https: http: ${
      process.env.NODE_ENV === 'production' ? '' : `'unsafe-eval'`
    };
    connect-src 'self' https://YOUR_FRONTEND_API_URL;
    img-src 'self' https://img.clerk.com;
    worker-src 'self' blob:;
    style-src 'self';
    frame-src 'self' https://challenges.cloudflare.com;
    form-action 'self';
  `
  // Replace newline characters and spaces
  const contentSecurityPolicyHeaderValue = cspHeader.replace(/\s{2,}/g, ' ').trim()

  // set the nonce and csp values in the request headers
  const requestHeaders = new Headers(req.headers)
  requestHeaders.set('x-nonce', nonce)
  requestHeaders.set('Content-Security-Policy', contentSecurityPolicyHeaderValue)

  const response = NextResponse.next({
    request: {
      headers: requestHeaders,
    },
  })

  response.headers.set('Content-Security-Policy', contentSecurityPolicyHeaderValue)

  return response
}

export const config = {
  matcher: [
    // Skip Next.js internals and all static files, unless found in search params
    '/((?!_next|[^?]*\\.(?:html?|css|js(?!on)|jpe?g|webp|png|gif|svg|ttf|woff2?|ico|csv|docx?|xlsx?|zip|webmanifest)).*)',
    // Always run for API routes
    '/(api|trpc)(.*)',
  ],
}

With this strict-dynamic configuration in place, all script tags must be passed with a nonce value or they will be blocked. This can be done by passing the nonce value as a nonce parameter to the script tag. For example, <script src="https://example.com/script.js" nonce="<nonce_value>"></script>. If you are using Next.js, any scripts loaded through next will automatically have the nonce value injected.

With the above middleware, the nonce value is made accessible via the x-nonce request header. An example is provided below on how to access this value within a Next.js page.

pages/index.tsx
import { headers } from 'next/headers'

export default function Page() {
  const nonce = headers().get('x-nonce')

  return <p>{nonce}</p>
}

If you're using one of Clerk's React-based SDKs, in order for Clerk to load correctly, the nonce value must also be passed to the <ClerkProvider> component. This can be done by passing the nonce value as a nonce prop to the <ClerkProvider> component. For example:

Important

You must pass the dynamic prop to <ClerkProvider> for strict-dynamic CSPs to work correctly. This is because the nonce value is generated on the server and passed to the client, which requires dynamic rendering.

app/layout.tsx
import { ClerkProvider } from '@clerk/nextjs'
import { headers } from 'next/headers'

export default function Layout({ children }) {
  return (
    // Note: since this is server-rendered, you don't _need_ to pass the nonce, see note below
    <ClerkProvider nonce={headers().get('x-nonce')} dynamic>
      <html lang="en">
        <body>{children}</body>
      </html>
    </ClerkProvider>
  )
}

If you are using Next.js and your layout file is rendered on the server (as is the case with the example above), Clerk's SDK will automatically read the nonce from the request and pass it into <ClerkProvider>. If you are rendering the provider on the client, you will need to explicitly pass the nonce value to the client and into <ClerkProvider>.

Feedback

What did you think of this content?
Edit this page on GitHub

Last updated on