[BUG] OAuth login fails with ERR_INVALID_IP_ADDRESS behind corporate proxy (regression since 2.0.37)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Environment

• Claude Code Version: 2.0.53
• Operating System: RHEL-based container (Dataiku Code Studio)
• Terminal: bash
• Platform: Anthropic API
• Node.js: 18.x
• Network: Corporate proxy (HTTP/HTTPS)

Bug Description

OAuth login fails with ERR_INVALID_IP_ADDRESS when running Claude Code behind a corporate proxy. The error occurs immediately when running claude or /login.

Error message:

Unable to connect to Anthropic services
Failed to connect to api.anthropic.com: ERR_INVALID_IP_ADDRESS

Key Finding: API Works, OAuth Doesn't

The network path to Anthropic is fully functional:

$ curl -v https://api.anthropic.com 2>&1 | head -20
* Uses proxy env variable https_proxy == 'http://b2b-http.dhl.com:8080'
* Connected to b2b-http.dhl.com (10.28.254.17) port 8080
* Proxy replied 200 to CONNECT request
# ... TLS handshake succeeds

API key authentication works:

$ export ANTHROPIC_API_KEY="sk-ant-..."
$ claude --print "hello"
Credit balance is too low  # ← Connection succeeded, just no credits

Only OAuth login fails with the IP address error.

Attempted Workarounds (None Worked)

| Attempt | Result |
|---------|--------|
| export NODE_OPTIONS="--dns-result-order=ipv4first" | No effect |
| export CLAUDE_CODE_OAUTH_TOKEN=<token from setup-token> | Still prompts for login |
| export ANTHROPIC_AUTH_TOKEN=<token> | No effect |
| Disable IPv6 via sysctl | Permission denied in container |

Working Workaround

Downgrading to v2.0.37 fixes the issue. A colleague using 2.0.37 behind the same proxy can login successfully.

npm install -g @anthropic-ai/claude-code@2.0.37
claude /login  # Works

Regression

• 2.0.37: ✅ Works behind corporate proxy
• 2.0.53: ❌ Fails with ERR_INVALID_IP_ADDRESS

Exact version where regression occurred is unknown (not tested: 2.0.38–2.0.52).

Expected Behavior

OAuth login should work behind corporate proxies when:

1. HTTPS_PROXY is correctly set
2. curl can reach api.anthropic.com through the proxy
3. API key authentication works

Related Issues

• #12081 - /login leads to invalid IP Address
• #12040 - OAuth authentication is currently not supported
• #11464 - OAuth authentication fails in proxy environment
• #332 - Claude Code unable to connect through corporate proxy in WSL

Additional Context

This appears to be a regression in how the OAuth flow handles DNS resolution or proxy tunneling. The underlying API connectivity is fine — only the OAuth code path is affected.

What Should Happen?

Claude Code VSCode extension should authenticate the session successfully.

Error Messages/Logs

Steps to Reproduce

Steps to Reproduce

1. Run Claude Code in a containerized environment behind a corporate HTTP proxy
2. Set HTTPS_PROXY=http://your-proxy:port
3. Run claude or claude /login
4. Observe ERR_INVALID_IP_ADDRESS error

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.0.37

Claude Code Version

2.0.53

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_