Providing access to existing web application from ownCloud client

I have a Web Application that stores data/files that I want to be accessible by the official ownCloud client (making my app behave like an ownCloud server). As far as I know ownCloud provides a ReST API that the ownCloud client consumes. Unfortunately I did not find any documentation for that ReST API yet.

Any hints on where to find this documentation? Or are there better solutions to provide access to my application via the ownCloud client?

Thanks in advance!