Microsoft Azure / Calendar API access

I have a project which needs to use OAuth2 to access Microsoft Calendar API. For this it seems I have set up an azure tenancy with Azure AD B2C so people with an outlook.com account for example can log in.
I need help with 2 things:

* verifying and setting up the Azure B2C tenancy with the correct APIs access so the app can read and write calendar events
* help with coding in Java to access the calendar and events

You will have to be very knowledgeable in Azure cloud and Java, especially in a Spring Boot environment and working with OAuth2.