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.

Installing

First, get Composer, then run:

composer require paragonie/csp-builder

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-to": "PolicyName",
    "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.

Processing output before save to disk through hook

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

The output will change before save to file

Support Contracts

If your company uses this library in their products or services, you may be interested in purchasing a support contract from Paragon Initiative Enterprises.

paragonie/csp-builder

paragonie

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