How to do authentication in a native app using web service?

In a web application, we have session to store the authentication. But let say I am developing a native application with web se开发者_Go百科rvice, for example, the Facebook app. How can I check the session in the native app? Thank you.

The way i know this can be done. Is by getting a hash key from the server once you are authenticated in the service. Then you can send back the key form the client each time you need to invoque a method during the session. That key will be invalidated by the server when session is expired or when you log out.