Not part of the template. You will have to add a small piece of code to show a password input box and once the user enters the correct password the app continues to next screen. More work will be required if you need to verify the username/password with a backend service.
Since you are using map viewer template just a quick heads up, we are completely rewriting the map viewer template to use the latest "quartz" v100.1 runtime and also undertaking major UI/UX redesign. It will look and work great. As part of that we will also support secured webmaps (i.e. the app will show UI to ask user of the app to enter his portal credentials to unlock the app) in addition to the current public webmaps.
