OAuth 2.0 is a major breakthrough in identity delegation. It has its roots in OAuth 1.0, but OAuth WRAP primarily influenced it. The main difference between OAuth 1.0 and 2.0 is that OAuth 1.0 is a standard protocol for identity delegation, whereas 2.0 is a highly extensible framework. OAuth 2.0 is already the de facto standard for API security and is widely used across leading web sites including Facebook, Google, LinkedIn, Microsoft (MSN, Live), PayPal, Instagram, Foursquare, GitHub, Yammer, Meetup, and many more. There is one popular exception: Twitter still uses OAuth 1.0.