Hey Brian,
If this dashboard is actually shared publicly, I would reach out to support. I tried access your dashboard using the generic url
Operations Dashboard for ArcGIS
And I am getting rejected when I am logged into my own ArcGIS Online account. This tells me that something is not shared at the Dashboard Level
I tried searching for the item id in ArcGIS Online and it did not appear.
My conclusion is that Dashboard id:419dfcfe8129410e91153c48efe99f32 is not actually shared and that is why you are seeing a sign in prompt!
Hope that helps!
-John