GitHub Copilot Authentication Failure on macOS Across Multiple Editors

Beginne damit, den Fehler mit :Copilot setup in copilot.vim zu reproduzieren, und vergleiche die Verarbeitung der Antwort mit dem funktionierenden Computer. Das Issue nennt keine Quelldateien oder Tests. Verfolge daher den Authentifizierungsablauf rund um den gemeldeten Fehler E-32603 und die Antwort ohne Content-Type. Als erledigt gilt die Aufgabe, wenn festgestellt wurde, ob die Ursache eine lokale Antwortmutation unter macOS oder eine vorgelagerte Änderung an der Authentifizierung ist, und ein reproduzierbarer Fix oder eine Diagnose dokumentiert wurde.

GitHub Copilot Authentication Failure on macOS Across Multiple Editors

Summary

GitHub Copilot authentication fails on one specific macOS machine across multiple editors/applications despite:

• clean network tests
• no proxy configured
• valid GitHub TLS certificates
• firewall/security tools disabled
• hotspot testing
• successful operation on another computer on the same network

The issue appears local to this Mac.

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Environment

Hardware / OS

• macOS
• Apple Silicon MacBook Pro (M4 Max)

Editors / Clients Affected

• Neovim + copilot.vim
• Zed

Versions

copilot.vim

copilot.vim 1.59.0
GitHub Copilot Language Server 1.485.0

Node

Initially tested with:

Node.js 24

Also tested with latest LTS Node.

---

Symptoms

Neovim / copilot.vim

Authentication fails during:

:Copilot setup 

Observed errors:

E-32603
Response content-type is missing (status=200)

and:

HTTP 200 response does not appear to originate from GitHub

---

Zed

• Unable to log into GitHub Copilot at all
• Inline predictions cannot initialize because auth never completes

---

Important Observation

A different computer on the SAME network can authenticate and use GitHub Copilot successfully.

This strongly suggests the issue is local to this specific Mac.

---

Network / TLS Diagnostics

Proxy Checks

env | grep -i proxy
git config --global --get http.proxy
git config --global --get https.proxy
npm config get proxy
npm config get https-proxy

Results:

No proxy configured
npm proxy values = null

---

System Proxy

scutil --proxy
networksetup -getwebproxy Wi-Fi
networksetup -getsecurewebproxy Wi-Fi

Results:

Enabled: No 

---

TLS / Connectivity Tests

GitHub API

curl -Iv https://api.github.com 

Results:

• Valid TLS
• Correct GitHub certificate
• HTTP/2 200
• content-type: application/json

Issuer:

Sectigo Public Server Authentication CA DV E36 

---

GitHub Device Login Endpoint

curl -Iv https://github.com/login/device/code 

Results:

• Valid TLS
• GitHub headers present
• HTTP/2 404 (expected for HEAD request)

---

Copilot API

curl -Iv https://api.githubcopilot.com 

Results:

• Valid TLS
• Correct GitHub Copilot certificate
• HTTP/2 404
• GitHub backend headers present

---

Remediation Attempts

Disabled Security Tools

• Firewall disabled
• Little Snitch disabled

No change.

---

Network Isolation

• Tested via hotspot

No change.

---

Cache Removal

Removed:

~/.cache/github-copilot
~/.cache/copilot.vim
~/.npm/_npx
~/Library/Application Support/Zed
~/Library/Caches/Zed
~/Library/Logs/Zed

No change.

---

Reinstalled copilot.vim

Original install was tarball-based.

Replaced with clean git clone:

git clone --depth=1 https://github.com/github/copilot.vim.git \
  ~/.config/nvim/pack/github/start/copilot.vim

No change.

---

Node Version Changes

Tested:

• Node 26
• Latest LTS

No change.

---

GitHub Auth Cleanup

• Revoked OAuth applications
• Cleared GitHub/Copilot-related Keychain entries
• Re-authenticated

No change.

---

Additional Notes

The error pattern appears similar to recent upstream reports involving:

Response content-type is missing (status=200) 

and Copilot auth parsing failures.

Potentially related upstream issues:

• github/copilot.vim issue #281
• similar reports involving copilot-language-server auth responses

---

Request

Looking for guidance on:

1. why this specific Mac receives/parses malformed auth responses
2. whether a recent Copilot auth backend change could trigger this behavior
3. additional macOS-level diagnostics for response mutation/auth parsing failures