Hi Adam and thanks a lot.
Ok I thought that it was .liquid files that was upload to shopify, packed as zip files and executed when somebody installed the app :-)
So I can use my microsoft server, jquery,html and javascript to build the app and to autenticate.
I guess it is like the facebook api!? They use oauth authentication.
Well I guess I just have to test and see how it goes, thanks again Adam.
If somebody have some more input I appreciate it.