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?

Replies

??? - 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?