We are looking for the easiest way to display a Main Calendar of events for our organization in SharePoint Online. The ideal scenario is users in our org will add the Main Calendar as an attendee to events they create in Outlook.
It appears adding an Exchange/Outlook calendar as an overlay in a SharePoint Online calendar does NOT work (I believe it does only in on-prem). The only real way I've found to do this without coding is on a SharePoint calendar choose 'Sync to Outlook', and then in Outlook copy the events over via list view. There are some paid apps in the office store but we are not interested in them.
Thus, we've been looking at the Graph API and possibly a SharePoint Framework web part (it looks you can call the Graph API with ADALjs in a SPFx webpart). Access to the Graph API requires an additional sign in step though so I'm not sure this is ideal if we have to have our users, inside sharepoint, sign in again to view the calendar. I've setup the simple NodeJS Graph API sample from the microsoft github but it required a sign in step. But if we want to display a calendar to users can we do this without requiring an additional sign in? Should we try to use the SharePoint Framework in combo with the ADALJS ? Or just deploy some js code that can connect to the Graph API in a CEWP?