expressjs/cors

Add ability to omit `Vary: Origin` header

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#317 opened on Mar 21, 2024

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enhancementhelp wanted

Description

Hello! Thank you to the authors and maintainers for this important package.

We have an issue where we would like the ability to conditionally omit Vary: Origin as a header. In our use case, we have specific routes for which the responses does not vary based on the requesting origin, e.g. a route for vending static image content.

Without this functionality, we are unable to use Cloudflare Polish1, which only accepts Vary: Accept-Encoding2, short of effectively rewriting all the cors code minus the Vary: Origin header.

Would this repository be able to add this functionality, or accept a patch to allow conditionally removing this header based on the requested routes?

Thank you again!

Footnotes

  1. https://developers.cloudflare.com/images/polish/ ↩

  2. https://developers.cloudflare.com/images/polish/cf-polished-statuses/ ↩

Contributor guide

Tech stack
javascriptnodejsexpress
Domain
backend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaScriptNode.jsExpress.jsCORS basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Examine the main source file (e.g., lib/cors.js) to understand how the Vary header is currently set. Review the existing options and their handling. Consider adding a new option that allows users to conditionally omit the Vary: Origin header. Look at the test suite to understand how tests are structured and add corresponding tests.