Content Security Policy Builder

Easily integrate Content-Security-Policy headers into your web application, either from a JSON configuration file, or programatically.

CSP Builder was created by Paragon Initiative Enterprises as part of our effort to encourage better application security practices.

Check out our other open source projects too.

There's also a CSP middleware available that uses this library.

Build a Content Security Policy header from a JSON configuration file

<?php

use \ParagonIE\CSPBuilder\CSPBuilder;

$csp = CSPBuilder::fromFile('/path/to/source.json');
$csp->sendCSPHeader();

You can also load the configuration from a JSON string, like so:

<?php

use \ParagonIE\CSPBuilder\CSPBuilder;

$configuration = file_get_contents('/path/to/source.json');
if (!is_string($configuration)) {
    throw new Error('Could not read configuration file!');
}
$csp = CSPBuilder::fromData($configuration);
$csp->sendCSPHeader();

Finally, you can just pass an array to the first argument of the constructor:

<?php

use \ParagonIE\CSPBuilder\CSPBuilder;

$configuration = file_get_contents('/path/to/source.json');
if (!is_string($configuration)) {
    throw new Error('Could not read configuration file!');
}
$decoded = json_decode($configuration, true);
if (!is_array($decoded)) {
  throw new Error('Could not parse configuration!');
}
$csp = new CSPBuilder($decoded);
$csp->sendCSPHeader();

Example

{
    "report-only": false,
    "report-uri": "/csp_violation_reporting_endpoint",
    "base-uri": [],
    "default-src": [],    
    "child-src": {
        "allow": [
            "https://www.youtube.com",
            "https://www.youtube-nocookie.com"
        ],
        "self": false
    },
    "connect-src": [],
    "font-src": {
        "self": true
    },
    "form-action": {
        "allow": [
            "https://example.com"
        ],
        "self": true
    },
    "frame-ancestors": [],
    "img-src": {
        "blob": true,
        "self": true,
        "data": true
    },
    "media-src": [],
    "object-src": [],
    "plugin-types": [],
    "script-src": {
        "allow": [
            "https://www.google-analytics.com"
        ],
        "self": true,
        "unsafe-inline": false,
        "unsafe-eval": false
    },
    "style-src": {
        "self": true
    },
    "upgrade-insecure-requests": true
}

Build a Content Security Policy, programmatically

<?php

use \ParagonIE\CSPBuilder\CSPBuilder;

$csp = CSPBuilder::fromFile('/path/to/source.json');

// Let's add a nonce for inline JS
$nonce = $csp->nonce('script-src');
$body .= "<script nonce={$nonce}>";
    $body .= $desiredJavascriptCode;
$body .= "</script>";

// Let's add a hash to the CSP header for $someScript
$hash = $csp->hash('script-src', $someScript, 'sha256');

// Add a new source domain to the whitelist
$csp->addSource('image', 'https://ytimg.com');

// Set the Report URI
$csp->setReportUri('https://example.com/csp_report.php');

// Let's turn on HTTPS enforcement
$csp->addDirective('upgrade-insecure-requests', true);

$csp->sendCSPHeader();

Note that many of these methods can be chained together:

$csp = CSPBuilder::fromFile('/path/to/source.json');
$csp->addSource('image', 'https://ytimg.com')
    ->addSource('frame', 'https://youtube.com')
    ->addDirective('upgrade-insecure-requests', true)
    ->sendCSPHeader();

• addSource()
• addDirective()
• disableOldBrowserSupport()
• enableOldBrowserSupport()
• hash()
• preHash()
• setDirective()
• setBlobAllowed()
• setDataAllowed()
• setFileSystemAllowed()
• setMediaStreamAllowed()
• setReportUri()
• setSelfAllowed()
• setAllowUnsafeEval()
• setAllowUnsafeInline()

Inject a CSP header into a PSR-7 message

Instead of invoking sendCSPHeader(), you can instead inject the headers into your PSR-7 message object by calling it like so:

/**
 * $yourMessageHere is an instance of an object that implements 
 * \Psr\Http\Message\MessageInterface
 *
 * Typically, this will be a Response object that implements 
 * \Psr\Http\Message\ResponseInterface
 *
 * @ref https://github.com/guzzle/psr7/blob/master/src/Response.php
 */
$csp->injectCSPHeader($yourMessageHere);

Save a CSP header for configuring Apache/nginx

Instead of calling sendCSPHeader() on every request, you can build the CSP once and save it to a snippet for including in your server configuration:

$policy = CSPBuilder::fromFile('/path/to/source.json');
$policy->saveSnippet(
    '/etc/nginx/snippets/my-csp.conf',
    CSPBuilder::FORMAT_NGINX
);

Make sure you reload your webserver afterwards.