authentication into theWire from stand-alone app

Hello everyone.

I just started with ELGG recently and my first target is theWire plugin. I'd like to enhance it with stand-alone application (probably written on flash) that will allow users to post and read the wire without accessing the site from the browser.

I have few problems I can't resolve without the opinion of experts.

Which is the best way to handle authentication from my application?
Should I use http headers or xml-rpc?
Or use API and auth inside the plugin?
What are pros&cons of each method?
Are there any other methods available?

Thanks for your responses,
Daniel.