Outlook

• Visit the Microsoft Outlook URL and complete the authentication
• Click the "calendar" from the sidebar on the right
• Click the "settings" button (the one displaying a cog) on the top-right side of the page
• Click the "View all Outlook settings" link on the bottom
• Access the Shared calendars section
• Select the calendar that you wish to export under the Publish a calendar section
• Under the authorization dropdown pick the option to see all the details
• Hit the Publish button to generate the export URL
• Copy the generated ICS URL (ignore the HTML version)

The resulting URL should look like this one:

https://outlook.live.com/owa/calendar/[A_LONG_SECRET_KEY]/[ANOTHER_SIGNATURE]/cid-[ANOTHER_SERIAL_CODE]/calendar.ics