SharePoint 2013 Apps Model comes with two types of authorization
- User + App Policy
- App Policy
User + App Policy
When SharePoint App uses this type of policy, both user and App must have permissions to access the resources such as list/library etc.
When this type of policy applies, only App must have permissions to access the resources, this is similar to the RunwithElevatedPrivileges method used earlier in the SP 2010 Farm solutions.
Authorization check succeeds only if the current app has sufficient permissions to perform the action in question, regardless of the permissions of the current user (if any).
To do such type of setting, Open the AppManifest.xml from the SharePoint App in Visual Studio 2012/2013 and navigate to the Permissions tab and select the “Allow the app to make app-only calls to SharePoint” checkbox as shown in the below screenshot.