Hi @sdnd2000,
Have you solved your problem?
Do you want to validate the user with AD authentication in the login screen?
Could you please share a bit more about your scenario?
Actually, each user who access to Power Apps is already validated with Active Directory by design. The User functions in Power Apps will give you access to that user's name, email, and department if you like.
In short, the Power Apps could not hold any password any time. The AD authentication has done everything related to validation before you access to the Power Apps app.
If you really want to achieve this in Power Apps, I think you should create a data source to hold the user info and validate it in canvas app.