Rewrite Client IP Enhancement Proposal

[kate-osborn]

Proposed changes

Problem:
As a user of NGF
I want to rewrite the client's IP address to the original client's IP
When fronting NGF with a LoadBalancer
So that the real client's IP address is forwarded to my application
Or so that I can log the client's IP address.

Solution: Add a design for rewriting the client's IP address

Closes #2328

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

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please add a brief note that summarizes the change.

NONE

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.74%. Comparing base (d014463) to head (2eda31f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2329   +/-   ##
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  Coverage   87.74%   87.74%           
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  Files          96       96           
  Lines        6830     6830           
  Branches       50       50           
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  Hits         5993     5993           
  Misses        780      780           
  Partials       57       57           

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[salonichf5]

great work 👏

[mpstefan]

Love the use case approach. Recursive is still weird, but I'm good with exposing it in the API as long as it's optional. NGINX directive approach sounds pretty similar to our NGINX customization that we plan to deliver next release, so I don't think we'd ever need to follow that pattern...

Thanks for the write-up, Kate!