2 factor authentication is a mechanism for adding a secondary security layer when logging in with a username and password. 

Logging in with Username and Password alone does not support the addition of 2 factor authentication.

If you require your users (or Admin users) to sign in with 2 Factor authentication you should integrate either Microsoft Office 365 or Google's G Suite, and use their authentication as the means to log into Appogee Leave/HR.  Those integrated office services will pass a pre-authenticated OAuth token across to Appogee Leave/HR to enable sign on, effectively ensuring 2 factor authentication has been respected.