Android :: Authenticating With Youtube - ClientLogin?

I'm writing an Android app that, among other things, uses the GData libraries to upload videos shot with the camera to Youtube (code below). However, I'm a bit confused about how to authenticate my users. Can I simply assume that they are already signed in to Youtube, since they're using Android? Or do I need to ask them to authenticate? In which case, should I use ClientLogin? There seems to be little example code on how to use ClientLogin in Android, and since it's using people's Google account passwords, it obviously needs to be secure. I'm a bit concerned at the prospect of writing my own authentication code without much guidance, and at the extra step required from users.

It seems odd that I have to ask people to authenticate for a Google service, given that they are using Google phones and the inbuilt Google apps don't require external authentication. Why is this? It seems to put my app at a disadvantage to Google's own apps.

Here's the code that I have, below:.....................