Greet user with His name "Hello ! XXX , This is Sara Bot "

How do we get user name without making him fill form about him or set slots? As in a welcome intent that says "Hello ! XXX , This is Sara Bot "

The tracker has a sender_id field. You have to make sure that each user has an unique id and some database with user information, including that id.

Ok but how will I know which user .Bot handles all conversation in general.I can get a table in db with user name ,id and his details but when I open the UI on website or telegram how will I get user info upfront