I want to implement login system where same user account can be used to login in different web applications. How can I achieve this ? I want to make a similar architecture to Google and Microsoft Account where different services can be used using the same account. I will be working in ASP.NET MVC for this. 
How to create a single login service to use it in multiple sites ? (similar to Google, Microsoft Account)
asp.net mvc;authentication;login;oauth2