unsafe-inline on script-src neutered CSP as an XSS defense on the login and OAuth
consent pages (the highest-value targets in an IdP). Switch to a per-response
nonce for both script-src and style-src and drop unsafe-inline entirely.
- Add a random per-response nonce generator and apply it to script-src/style-src.
- Remove :unsafe_inline from both directives.
- Nonce the one hand-written inline script (dark-mode detection in the layout).
- Convert the 2 static style="display:none" attributes to class="hidden" (their
runtime toggle is done via element.style in JS, which CSP does not govern).
importmap-rails (2.2.3) already stamps the nonce onto its generated inline
importmap/module/preload tags, and Turbo (2.0.23) reads csp_meta_tag for its
injected <style>, so no other view changes were needed. Adds an integration test
asserting the enforcing header carries nonces, omits unsafe-inline, and that the
inline script's nonce matches the header.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
d49e7ce4f5