A [content security policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) (CSP) adds an important layer of security to your web app by helping to mitigate cross-site scripting and data injection attacks. It enforces what content is loaded in your app. This includes images, CSS, fonts, scripts, network requests, and more.
This guide describes how you can set up and customize a CSP for your site.
## What you'll learn
In this tutorial, you'll learn how to do the following tasks:
- Setup a Content Security Policy on an existing Hydrogen app.
- Define custom directives within your Content Security Policy.
- Secure third party scripts with a Content Security Policy nonce.
## Requirements
- You've completed the Hydrogen Getting Started with a Hello World example project.
## Step 1: Set up a content security policy
Hydrogen provides a default content security policy. Add the content security policy by using the [`createContentSecurityPolicy` utility](/docs/api/hydrogen/utilities/createcontentsecuritypolicy) within your `entry.server.jsx` file which returns:
- `nonce`: Pass this value to React's `renderToReadableStream` or any other custom component that renders a script under the hood.
- `NonceProvider`: This makes the nonce available throughout the app, and renders it by wrapping `RemixServer`.
- `header`: This is the actual content security policy header value. Add it to your app response headers.
Your updated `entry.server.jsx` should look something like the following:
## Step 2: Add a nonce to your scripts
If you start your app's server, you'll notice a lot of errors in the console and scripts will fail to load. This is because the `nonce` value also needs to be passed to each script in the app.
1. Update `root.jsx` to use the [`useNonce()` hook](/docs/api/hydrogen/hooks/usenonce) and pass the value to the `ScrollRestoration`, `Scripts`, and `LiveRelod` components. Make sure to also update the error boundary:
2. If you use any third-party scripts, then use the [`Script` component](/docs/api/hydrogen/components/script) which automatically attaches the `nonce`:
## Step 3: Customize the content security policy
You can extend the default CSP generated by Hydrogen by passing [custom directives into `createContentSecurityPolicy`](/docs/api/hydrogen/utilities/createcontentsecuritypolicy#props-propertydetail-directives). Refer to the [content security policy reference](https://content-security-policy.com/) for a description of available directives.