OAuth is an HTTP-based authorization protocol. It gives third-party applications scoped access to a protected resource on behalf of the resource owner. It gives scoped access by creating an approval interaction between the resource owner, client, and the resource server. It gives users the ability to share their private resources between sites without providing usernames and passwords. Private resources can be anything, but common examples include photos, videos, and contact lists.
OAuth 2.0 is a simple protocol that allows accessing resources of the user without sharing passwords.
It accesses the data using tokens instead of using their credentials and stores data in the online file system of the user such as Google Docs or Dropbox account.