GitHub Copilot Authentication Failure on macOS Across Multiple Editors

# 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.

---

# Environment

## Hardware / OS

- macOS
- Apple Silicon MacBook Pro (M4 Max)

## Editors / Clients Affected

- Neovim + copilot.vim
- Zed

## Versions

### copilot.vim

```text
copilot.vim 1.59.0
GitHub Copilot Language Server 1.485.0
```

### Node

Initially tested with:

```text
Node.js 24
```

Also tested with latest LTS Node.

---

# Symptoms

## Neovim / copilot.vim

Authentication fails during:

```vim
:Copilot setup
```

Observed errors:

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

and:

```text
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

```bash
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:

```text
No proxy configured
npm proxy values = null
```

---

## System Proxy

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

Results:

```text
Enabled: No
```

---

## TLS / Connectivity Tests

### GitHub API

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

Results:

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

Issuer:

```text
Sectigo Public Server Authentication CA DV E36
```

---

### GitHub Device Login Endpoint

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

Results:

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

---

### Copilot API

```bash
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:

```bash
~/.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:

```bash
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:

```text
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