Support native subscription OAuth login for ChatGPT and Claude

[Yeachan-Heo]

Request

Add first-class OAuth / browser-login auth flows for using existing ChatGPT and Claude subscriptions directly in Claw Code, instead of requiring API keys only.

Motivation

Some users already pay for ChatGPT Plus/Pro/Team or Claude Pro/Max/Team and want to use those subscription entitlements natively from the CLI, similar to first-party coding-agent products, without paying again through API billing.

Desired behavior

• claw auth login chatgpt or equivalent starts a safe browser/device-code OAuth flow.
• claw auth login claude or equivalent starts a safe browser/device-code OAuth flow.
• Auth state is stored in the existing secure config/credential path, not in project files.
• Provider selection can use the logged-in subscription provider when available.
• Clear errors distinguish subscription auth from API-key auth.
• Logout/revoke flow exists.

Non-goals / constraints

• Do not rely on scraping private web session cookies or brittle browser-profile copying.
• Do not ask users to paste tokens from browser devtools.
• Respect provider terms and only implement flows that are supportable and maintainable.
• Keep API-key auth working exactly as-is.

Acceptance criteria

• A documented CLI flow exists for ChatGPT subscription login and Claude subscription login, or a documented reason one/both cannot be supported safely.
• Auth errors clearly tell users whether they are using API-key auth or subscription OAuth auth.
• Tests cover config isolation, logout, missing/expired token handling, and provider selection fallback.

Requested from the UltraWorkers #claw-code community thread.