Parse SDK doesn't obey `ETag` header from express server

[kassiansun]

New Issue Checklist

• [x] I am not disclosing a vulnerability.
• [x] I am not just asking a question.
• [x] I have searched through existing issues.
• [x] I can reproduce the issue with the latest versions of Parse Server and the Parse ObjC SDK.

Issue Description

Currently, parse-server will return ETag header for /parse/* requests, but the client is not caching it properly

Steps to reproduce

/parse/config returned ETag header, but the parse client is not sending If-None-Match along with the further requests to /parse/config

Actual Outcome

Expected Outcome

The client should obey the standard HTTP caching semantics, and re-use local cache if the ETag is consistent with remote version: https://www.rfc-editor.org/rfc/rfc9111.html

Environment

Client

• Parse ObjC SDK version: 2.7

Server

• Parse Server version: 5.6.0
• Operating system: Ubuntu 22.04
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): AWS

Database

• System (MongoDB or Postgres): MongoDB
• Database version: 5.0
• Local or remote host (MongoDB Atlas, mLab, AWS, Azure, Google Cloud, etc): AWS

Logs

[parse-github-assistant[bot]]

Thanks for opening this issue!

• 🚀 You can help us to fix this issue faster by opening a pull request with a failing test. See our Contribution Guide for how to make a pull request, or read our New Contributor's Guide if this is your first time contributing.

[kassiansun]

Here it says "for security reasons", is this still valid nowadays? The code was introduced at 2015: https://github.com/parse-community/Parse-SDK-iOS-OSX/blob/master/Parse/Parse/Internal/Commands/CommandRunner/URLSession/Session/PFURLSession.m#L261