Distributed systems are widely used now-a-days. In the advent of mobile technology, their existance become more important. Data are handled with API with secure channel.
Oauth 2.0 is very secure for authentication system. Every big companies now implementing Oauth 2.0 for their system.
Oauth 2.0 doesn’t mean login with social networks. Oauth 2.0 is a process for authentication system. Yes, most of the popular social network sites have implemented this feature. But if you want to make this feature available for your site also, then you need to follow their proposed methodologies. Currently, there are many libraries available in different languages. You can get your preferred one.
Tahsin Hasan is very experienced on authentication architecture. He implemented many sophisticated authentication system for distributed and mobile applications. He is available at tahsin352(at)gmail(dot)com.