Auth2 implementation for JAVA EWS existing project

Question

I am new to auth2 implementation for Microsoft Exchange service and I want to implement the same in existing process Login Process. Previously we are using Username password technique to create EWS object. Now I want to update existing Username and Password technique with Auth2 Process.

As of now I have try to used Graph API to Generate Access Code using below link

https://docs.microsoft.com/en-us/graph/tutorials/java

But Facing issue: The request body must contain the following parameter: 'client_assertion' or 'client_secret'.

Using another library as below for auth2

https://github.com/AzureAD/microsoft-authentication-library-for-java/wiki

This library also facing some issue like Collection$Singleton object not able to cast java.lang.String

While passing scope

Please suggest me some sample for to implement the AUTH2 implementation for the EWS in java.