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fix: handle immutable headers returned by native fetch in middleware #589

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fix: handle immutable headers returned by native fetch in middleware #589

Kakadus wants to merge 1 commit into from
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@Kakadus Kakadus commented Jan 27, 2026

Related Issue or Design Document

Close #588

On nodejs, the headers returned by fetch are immutable, following the whatwg standard. In the nextjs middleware, this leads to an TypeError when proxying e.g. POST login requests to kratos.

This clones the headers object before modification, preventing the error.

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  • I have read the contributing guidelines and signed the CLA.
  • I have referenced an issue containing the design document if my change introduces a new feature.
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  • I confirm that this pull request does not address a security vulnerability.
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    I confirm that I got approval (please contact security@ory.sh) from the maintainers to push the changes.
  • I have added tests that prove my fix is effective or that my feature works.
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changeset-bot bot commented Jan 27, 2026 •
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Latest commit: 832a8a1

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codecov bot commented Jan 27, 2026 •
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Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.02%. Comparing base (f3fad4d) to head (832a8a1).
⚠️ Report is 281 commits behind head on main.

Additional details and impacted files 
@@             Coverage Diff             @@
##             main     #589       +/-   ##
===========================================
+ Coverage   42.43%   56.02%   +13.59%     
===========================================
  Files         136      174       +38     
  Lines        2008     3259     +1251     
  Branches      288      481      +193     
===========================================
+ Hits          852     1826      +974     
- Misses       1149     1358      +209     
- Partials        7       75       +68
Components Coverage Δ
@ory/elements-react 54.92% <ø> (+18.13%) ⬆️
@ory/nextjs 62.60% <ø> (-3.38%) ⬇️
🚀 New features to boost your workflow:
  • 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

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Kakadus commented Jan 27, 2026 •
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The formatting CI error is only on unrelated files. The codecov report also looks sketchy to me, as all lines are clearly executed / are in tests.

@Kakadus Kakadus changed the title fix(nextjs): handle immutable headers returned by native fetch in middleware fix handle immutable headers returned by native fetch in middleware Jan 27, 2026
@Kakadus Kakadus changed the title fix handle immutable headers returned by native fetch in middleware fix: handle immutable headers returned by native fetch in middleware Jan 27, 2026
jonas-jonas
jonas-jonas approved these changes Jan 28, 2026
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Thank you! Looks reasonable to me.

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@jonas-jonas jonas-jonas jonas-jonas approved these changes

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TypeError: immutable in nextjs middleware when deleting headers from upstream response

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