I am new in iphone application. I want to make a simple application in which User can login from google and facebook. I have integrate API's for both of them. I have also completed the facebook connection but I dont know how to validate the Google user with its API (Gdata). Can anybody please help me for authentication of google account using iphone application.I just want to check wether user is valid google user or not that's it. Please help me for that. Thanks in advance..
Google supports OpenID, though that is typically just used by websites.
There is also authentication for Google accounts called ClientLogin; the Objective-C GData library provides routines to authenticate via ClientLogin to a Google account for use with a specific Google service API.
What is it that your application will do for authenticated users that it would not do for unauthenticated users?
来源：https://stackoverflow.com/questions/1958188/how-do-i-authenticate-a-google-user-on-the-iphone-using-gdata