username password for testers to log in to app in order to review app

If I require the testers to sign in with a username and password to review my app, where in Xcode do I set that up?

??? - There is TestFlight in iTunes Connect, begin there ...

That's the one I'm speaking of. I thought I would have to set another username and password in Xcode. Is the username and password to be used by testers in order to install the app?

username password for testers to log in to app in order to review app
 
 
Q