How we can use OAuth for log into social sites in K2.......

Hi - two answers to your questions, sorry for a late reply but I'm not on these forums too often.

1) Using OAuth is mostly around configuring the necessary OAuth resources for the system you want to integrate with. This is covered in the following K2 KB article: http://help.k2.com/kb001702#

Note that OAuth authentication mode is broker-specific and only certain brokers support the use of OAuth, such as the EndPoints WCF and EndPoints Web Service brokers.

2) Regarding REST integration: K2 is running a beta program of a new REST Service Broker to allow interacting with REST services and endpoints as SmartObjects. To join the beta program, please email beta@k2.com and once you've joined the program, you can obtain the necessary resources from http://help.k2.com/restbeta

There are many resources in the beta progrma to explain how to integrate with a rest service.

Cheers

Neil