User and App Identity in SharePoint 2013 Apps

According to MSDN http://msdn.microsoft.com/en-us/library/fp179892.aspx Apps in SharePoint can operate using 3 different authorization policies: 1. User-Only policy 2. User + App policy 3. App-Only policy Read more: http://www.dshift.com/blog/user-and-app-identity-in-sharepoint-2013-apps/