[8.4-stable] feat(csp): send a Content Security Policy with admin responses - #4238
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Alchemy now sends a Content Security Policy with its own admin responses, so a mistake that renders content unescaped stays a display bug instead of becoming script execution in an editor's session. It is on by default, for new installations and for upgrading applications alike, because the admin surface Alchemy ships works under it entirely. The option is documented in the configuration template, so it reaches existing applications through alchemy:upgrade:config, and the upgrader raises a todo pointing at it for the rare application that does have inline scripts in admin views of its own. The policy is built by a configurable class. Alchemy fills in the host dependent sources from what it already knows: the asset host, the preview hosts the page editor loads into an iframe, admin stylesheets served from another host, and modules pinned to a CDN. Anything beyond that is a subclass away. It only applies to Alchemy's own controllers, never to host application controllers inheriting from the admin base class, and it is skipped entirely when the host has configured a policy of its own. The csp-nonce meta tag is added unconditionally because Turbo reads the nonce from it to authorize the style element it injects for the progress bar. It renders nothing when no policy is configured. (cherry picked from commit f0c2ff9)
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## 8.4-stable #4238 +/- ##
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+ Coverage 98.36% 98.37% +0.01%
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Files 360 361 +1
Lines 9580 9644 +64
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+ Hits 9423 9487 +64
Misses 157 157
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tvdeyen
approved these changes
Sep 8, 2026
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