Add AntiforgeryOptions.AllowBackForwardCache - #68738
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By default the antiforgery system sets Cache-Control: no-cache, no-store on responses that carry a token. Browsers treat no-store as opting the response out of the back/forward cache, so navigating back re-fetches the page from the server. Add an opt-in AntiforgeryOptions.AllowBackForwardCache. When set, the header is no-cache, private instead, which keeps the response out of shared caches while allowing the browser's back/forward cache. The default is unchanged. Fixes dotnet#54464
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Summary
Fixes #54464. By default the antiforgery system sets
Cache-Control: no-cache, no-storeon responses that carry a token (DefaultAntiforgery.SetDoNotCacheHeaders). Browsers treatno-storeas opting the response out of the back/forward cache, so using the back button re-fetches the page from the server, which is slower and shows up as a page diagnostics warning.Change
Add an opt-in
AntiforgeryOptions.AllowBackForwardCache(defaultfalse, so existing behavior is unchanged). When set totrue, the header becomesCache-Control: no-cache, privateinstead ofno-cache, no-store: droppingno-storelets the browser use the back/forward cache, andprivatekeeps the response out of shared caches.This follows the triage note on the issue, which suggested marking the header
privateto avoid storage in shared caches. I kept it opt-in so the default does not change and no existing behavior regresses. If you would rather change the default instead (the triage note mentioned that is reasonable, pending browser end-to-end testing), I am happy to adjust.Testing
Added tests to
DefaultAntiforgeryTestverifying that with the option set the header isno-cache, private, and that an existingno-cache, no-storeheader is replaced, while all existing tests for the defaultno-cache, no-storebehavior continue to pass. The full Antiforgery test suite (187 tests) passes on Linux and Windows.