ASP.net web application user id fetch

He team,
I have asp.net web application which has login form … which get 3 inputs like username , password and domain. Based on user id fetching employee details from database… now integrating with okta same application but I need okta user ID is same as employee (user id) .but unable to get okta user id into application
Please help me.
Configuration :asp.net 3.5 framework (vs2010)