Hi Arman
I have not worked with the users in AEM for very long time. But I don't believe anything might have deprecated much in last 2 years. I could find some documentation for you from the Internet.
Please read the below blogs and I believe this can help.
How to get the UserInfo through Java API in Adobe CQ5
You can use memberOf() method of the User (Adobe AEM 6.0.0 API 6.0.0 API) and Authorizable (Adobe AEM 6.0.0 API 6.0.0 API)
This will return you the list of groups the user is added to
Thanks
Veena