Poll and exchange an approved CLI login

Poll no faster than the returned interval. authorization_pending means continue; slow_down permanently increases the interval by five seconds (also reflected in Retry-After). Stop for access_denied, expired_token, or invalid_grant. On approval, current membership, project status and organization key limits are checked again. The grant mints a normal signed API key once, expiring after thirty days. There is no refresh token or replay: if a successful response is lost, restart login. The key can be revoked from the console.