How to have a native android app authenticate with web backend?

[whorobj]

I'm working on developing a native android application to retrieve data for a user from my company's website.Because the data is specific to the user, I need to authenticate with our web server, but I'm unsure of the best way to go about this. I've been reading about REST/SOAP/HTML form auth, but I can't really find any definite 'this is how its done' anywhere. I know mobile apps do this kind of thing all the time - just look at facebook/skype/any email app - you have to login before you can do anything.My question is - how should I architect the server side code (php) to easily allow me to authenticate a user from my android device?I'm fairly new to the 'web service' arena - does this fall into that category? Are there any tutorials you guys would recommend looking at?Thanks!