If I visit https://circleci.com/gh/cjw296/workflows/playground/tree/master when not logged in, I get a partially rendered page with no content.
This is a public, open source project and I'd expect people who haven't logged in to CircleCI to still be able to view workflows and their results...
Looks like other people have hit this too and feel it might even be classed as a bug:
This likely has a lot of overlap with https://ideas.circleci.com/ideas/CCI-I-569.
Why might CircleCI want to do this? Well, it's a lot easier for me to sell CircleCI for commercial use to people when they don't have to log in to see some sample output!