Who Are You Anyway?
Social sign-in adds an extra twist to sign-in on the web. While systems like OpenID are often used purely to assert identity (e.g. you are the same person as when you came here before), OAuth and OAuth 2.0 were always about granting access to data (e.g. you give me permission to know who your name and friends). While both of these get to the same place for most developers - someone can log in, and you can reliably and securely know which user in an application they map to - the difference is largely about what other data is available.Most social sign-in systems grant access to profile information, such as name, gender, email address, age or age range, and other more specific information. They often also grant access to a users activities on the identity provider, either explicitly or implicitly: for example if I sign in with Google+ you can retrieve a list of the people I have circled (or at least the ones I have given you access to), or if I sign in with Twitter you can easily get a …