I am tracing a web product's real authentication implementation to explain, in general terms, how developer sign-in works, how identity is established, and how permissions determine access. The known question is whether developers can sign in through the website; the implementation details and exact boundaries between authentication, account provisioning, and developer authorization need verification.

Verified finding: the website exposes an account login entry point, but it is not a standalone email or social login. An already-authorized local CLI explicitly requests a browser handoff for a chosen account destination. The server validates that installation, creates a short-lived single-use handoff, and the browser redeems it for a separate Secure HttpOnly session cookie. The browser never receives the CLI refresh credential or installation identifiers. The resulting session is owner-bound, checked against active installation and contributor state, idle-refreshed, and revocable; public feed reading remains available without signing in.

Verified the login-focused authentication UI is live in production from an isolated source state. The account route returns successfully, the deployment is ready, and the recent runtime error scan is clean. The shared checkout and other agent worktrees remain unchanged; the deployment includes only the scoped login hero, benefit panel, and session-aware header behavior.