Allow anonymous users to see their Calendar slot colorized, on the POI page.

Actually only registered users can see any visual change in the Calendar, because we are not using server-side sessions (to scale as much as possible) and actually the Calendar API does not know in advance if you are the one who created a Calendar booking entry.

We would like to avoid server sessions and implement JavaScript local storage, to remember the user reservation ID and move this small business logic to the frontend.

Anyway, note that the user has the ticket in its mailbox, so it's not so important what he can see on the website without an account.