Comment 5 for bug 1192704

Hi Kai, we don't have a tutorial on how to do it, but fortunately it's not a hard task (usually :-) ).
It seems like App.net uses OAuth 2.0, and I'd recommend going for the client flow described here:
http://developers.app.net/docs/authentication/flows/web/#client-side-flow

You can start by working on the desktop first (it's slightly easier, and you can reuse all your work for Ubuntu Touch later on): take the /usr/share/accounts/providers/facebook.provider file, rename it to "appnet.provider" and edit it to use the URLs and scopes defined by app.net.
You can then try to create an account in the control center, and see if that works. You are very welcome to get in touch with me (mardy) in #ubuntu-devel or #ubuntu-touch on IRC. Or just comment here.