You can find the postmortem here.

The sign-in experience has recovered.

Cause: During a recent deployment, a breaking database schema change caused an exception when swapping between the staging and production environments.

We apologize for any inconvenience this may have caused. We are currently discussing and planning preventative measures to ensure this issue does not occur again in the future. These measures will be implemented as soon as possible.

The sign-in experience shows error code 500.