This issue is now resolved. Our identity provider has fixed the problem, and dashboard access is back to normal for all users.

We've confirmed the issue is with our identity provider, which handles sign-in to the dashboard. We're in contact with them to resolve it and will post another update as soon as we have one.

We're aware that a small number of users are having trouble accessing the dashboard. We're investigating and will post an update as soon as we know more.