Putting csp_whitelist.xml in theme does not work and creates intermittent issue

[Jakhotiya]

Preconditions and environment

• 2.4.7 and 2.4-develop

Steps to reproduce

• Put csp_whitelist.xml under your frontend theme's etc/ directory. (You can put this in Luma theme too. Just any theme will work)
• Clear your cache
• Without doing anything else Open your admin page
• now open frontend and check csp headers

Expected result

Domains listed in your custom csp_whitelist.xml under theme should have reflected on frontend

Actual result

If admin is hit first after cache flush, domains under your csp_whitelist.xml under theme are not seen on frontend.

Additional information

This bug happens because contents of csp_whitelist.xml in theme are stored in global cache.
Lets see how this works right now.
CSP cache is maintained area wise. For example, you will find 3 files in your cache

var/cache/mage--8/mage---06a_FRONTEND__CSP_WHITELIST_CONFIG
var/cache/mage--2/mage---06a_GLOBAL__CSP_WHITELIST_CONFIG
var/cache/mage--a/mage---06a_ADMINHTML__CSP_WHITELIST_CONFIG

Now the bug happens because of app/code/Magento/Csp/Model/Collector/CspWhitelistXml/FileResolver.php

public function get($filename, $scope)
    {
         $configs = $this->moduleFileResolver->get($filename, $scope);
        if ($scope === 'global') {
            $files = [];
            $theme = $this->theme;
            while ($theme) {
                /** @var CustomizationInterface $info */
                $info = $this->themeInfoFactory->create(['theme' => $theme]);
                $file = $info->getThemeFilesPath() .'/etc/' .$filename;
                if ($this->rootDir->isExist($file)) {
                    $files[] = $file;
                }
                $theme = $theme->getParentTheme();
            }
            $configs = $this->iteratorFactory->create(
                ['paths' => array_reverse($files), 'existingIterator' => $configs]
            );
        }

        return $configs;
    }

if ($scope === 'global') leads to csp_whitelist config in theme being put in global cache.
After cache flush if admin request lands on server, $theme variable is set to Magento/backend .
In this case, your file in frontend theme wont be read. Global cache is then populated according to Magento/backend

The behavior completely depends on which area request lands first, frontend or admin. This leads to poor developer experience too.

Release note

No response

Triage and priority

• Severity: S0 - Affects critical data or functionality and leaves users without workaround.
• Severity: S1 - Affects critical data or functionality and forces users to employ a workaround.
• Severity: S2 - Affects non-critical data or functionality and forces users to employ a workaround.
• Severity: S3 - Affects non-critical data or functionality and does not force users to employ a workaround.
• Severity: S4 - Affects aesthetics, professional look and feel, “quality” or “usability”.

[m2-assistant]

Hi @Jakhotiya. Thank you for your report.
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[m2-assistant]

Hi @engcom-Hotel. Thank you for working on this issue.
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[engcom-Hotel]

Hello @Jakhotiya,

Thanks for the report and collaboration!

We have tried to reproduce the issue in the latest development branch i.e. 2.4-develop and the issue has been reproducible for us.

Please refer to the below screenshots for reference:

In case after clearing cache access the admin panel and then access the frontend

In case after clearing cache directly access the frontend

Hence confirming the issue.

Thanks