Restfulyii For Web Service

I have a Web application where users can login and post some data. Now I want to create REST API for that application so that it can be consumed by an android mobile app.

I found that using restfulyii extension I can create REST APIs easily. But I dont know how to authenticate each user from my Android app using restfulyii extension. Can anyone tell me how to do that with example? I’m using mongoDB for storing the data. Thanks in advance.