Issue - iCloud - Mac - Web - authentication

1. Log into the iCloud web app from a mac machine (10.11.4)
2. Click "Pages"
3. Journey progresses for an instant but a further round of authentication commences, which subsequently fails, re-directing back to the original login page
4. No progression seems possible
5. 😕

Does anyone else experience this and is there a resolution?

Thanks 🙂