Got to work on this task and I found this link to be helpful:

Building Daemon or Service Apps with Office 365 Mail, Calendar, and Contacts APIs (OAuth2 client credential flow)

There is another sample codes which allows retrieval of calendars from shared calender:
https://code.msdn.microsoft.com/office/How-to-Search-Calendar-ef882136

Original source for both of the articles:
https://stackoverflow.com/questions/37116762/office-365-outlook-calendar-how-to-access-multiple-users-calendar-in-a-single?noredirect=1&lq=1