## Why
Gateway sign-in needs an alternative for terminals that cannot open a browser.
## What changed
- Add optional `gateway_oauth.device_authorization_url` configuration and a `login_with_device_code` API that presents a verification URL and user code, polls for approval, and persists the resulting credentials.
- Use the configured proxy and network policy, validate verification URLs, and bound OAuth responses. Support cancellation and report denied or expired codes without exposing issuer error details.
## Testing
Add tests for successful authorization and credential persistence, unsafe verification URLs, network-policy denials, denied and expired codes, and cancellation during approval or credential storage.
GitOrigin-RevId: 96398578fb866d34929e85c04eadf468d8cd3255