I was trying to understand how to integrate a product with Qlik,
doing stuff like listing apps, finding app configurations, data values etc. I think that most of the Engine API does that, the getting started page doesn't really explain how to connect, but the main Engine API page shows that I should connect to a Qlik Sense Proxy Service.
But, the proxy service says that it's a REST api and the engine api says you need a websocket connection here.
So if I have to make some API calls to the Qlik cloud sense, which one of those API should I use? How do I authenticate?
Can someone please explain briefly what the steps should be?
The proxy has a REST api for doing operations on the proxy it self. The engine API, on the other hand, is based on JSON RPC through websockets. You might also want to have a look at the Repository API (also REST based) which you can use for instance to list apps on the server. The end point for listing apps can be found here: App: Get hub list ‒ Qlik Sense
Based on your question, it sounds like you want to investigate the contents of apps as well. In that case you have to go through the engine API. How to connect depends on your environment, but one possibility is to use the .Net SDK which has been designed to access the engine API through C#. It's available for download from NuGet: https://www.nuget.org/packages/QlikSense.NetSDK/