Copilot /login fails with "fetch failed" behind corporate proxy while gh auth succeeds, logs show "Github CLI authenticated with valid token" but no error details

[vkoppara]

Describe the bug

I can authenticate Github CLI (gh) using a new fine-grained PAT over https.
Copilot /login still fails with "Error during sign-in: fetch failed".
Logs only show "Github CLI authenticated with valid token" and no further details
Environment is behind a corporate proxy with Kerberos negotiation; I'm using a local px-proxy (python) bridge to make gh work.

Affected version

0.0328 Commit: 3755a93

Steps to reproduce the behavior

Setup http(s) proxy through corporate proxy (kerberos)
Use px-proxy locally; run gh auth login with fine-grained PAT -> succeeds.
Run copilot /login -> shows "Error during sign-in: fetch failed".

OS: macOS
Node Version: v22.19.0 & also tried with v24.9.0 (with NODE_USE_ENV_PROXY=1)

Expected behavior

copilot /login succeeds using the same networking/proxy setup.
Or logs provide actionable diagnostics (proxy/TLS/Auth) to troubleshoot.

Additional context

What I tried:
Confirmed gh auth works via px-proxy
Verified PAT scopes (repo, read:org, workflow)
Confirmed HTTPS protocol and base host github.com

** gh auth login **
@ log % gh auth login
? Where do you use GitHub? GitHub.com
? What is your preferred protocol for Git operations on this host? HTTPS
? Authenticate Git with your GitHub credentials? Yes
? How would you like to authenticate GitHub CLI? Paste an authentication token
Tip: you can generate a Personal Access Token here https://github.com/settings/tokens
The minimum required scopes are 'repo', 'read:org', 'workflow'
? Paste your authentication token: ***********************************************
-gh config set -h github.com git_protocol https
Configured git protocol
Logged in as

** Copilot Logs **
@ %cat log/.log
2025-10-02T03:27:36.494Z [START-GROUP] gh auth token --hostname github.com
2025-10-02T03:27:36.496Z [START-GROUP] gh auth token --hostname github.com
2025-10-02T03:27:36.658Z [DEBUG] ******

2025-10-02T03:27:36.658Z [END-GROUP]
2025-10-02T03:27:36.659Z [DEBUG] GitHub CLI authenticated with valid token
2025-10-02T03:27:36.664Z [DEBUG] ******

2025-10-02T03:27:36.664Z [END-GROUP]
2025-10-02T03:27:36.664Z [DEBUG] GitHub CLI authenticated with valid token

I also tried with the following steps:

1. gh auth logout
2. export GH_TOKEN=
3. copilot --log-level debug --log-dir ./log (& /login)
4. still same issue (with "GitHub CLI authenticated with valid token" in the copilot log)

[devm33]

De-duplicating with #41

See #41 (comment) for latest update

[vkoppara]

I checked #41, it still did not work for me.