Blocking Employee Outlook Calendar for Absence Dates

one of our customers has a requirement to block employee calendars when they apply for leave. For example, if the employee has an approved leave in the Oracle system for the 30th of November. Then those leave dates should be blocked in the Outlook calendar as well. 

Currently, Employees can download ICS files and import them to the outlook. However, the requirement is to automate this process. 

please guide us on this whether there is a way to achieve this or if any APIs or Pre-build option is available.