NOTE: this is obsolete, calendar authorization app can be installed only by tenant administrator. To overlay Calendars from different Site Collection...

We have created an App with same ID that you can install in your tenant App Catalog. https://download.virtosoftware.com/dev/Calendar_ProviderHosted.app

After installing Calendar App you can use it for all SharePoint data sources from current Site Collection without additional prompt to install Calendar Auth...

Calendar App uses delegated permissions to access Exchange data and SharePoint data from different site collections. https://docs.microsoft.com/en-us/azu...