Node.js client api key

I have a node.js backend for an ios app that will provide json data to the app. I want to handle client authentication for each app. The users do not need to create an account. I only want to identify the client apps when providing data and save some data for each client on the node server.

1. How do I handle identifying each app on the server?
2. If I need to create an API key, how do I handle that?
3. If there is a way to authenticate the app when the app first accesses the API, how can I create a unique identifier for the app?
4. Last, what do I need to know before I deploy the node server? Can I get away by just pointing a domain to my router, opening a port and serving the api from there or is it a must to have a web server setup to handle that?

Thank you

via tew