OAuth needed for a simple front end project? (twitch.tv embed)

I am trying to make a site that embeds one twitch channel.

Users will be able to login and use the chat feature and post emotes in twitch chat.

Nothing more than that.

The layout is something like this:

which is really simple. And I want the site to be responsive. For example, when the viewport is really narrow, chat will appear below main video feed.

So my question is this: Do I need a backend for a site like this? Use OAuth to prompt users to log in?