Breaking changes in SQL Server Reporting Services in SQL Server 2016
Applies to: 
SQL Server Reporting Services (2016) ❌ SQL Server Reporting Services (2017) ❌ Power BI Report Server
For content related to previous versions of SQL Server Reporting Services (SSRS), see What is SQL Server Reporting Services?
This topic describes breaking changes in Reporting Services. These changes might break applications, scripts, or functionalities that are based on earlier versions of SQL Server. You might encounter these issues when you upgrade, or in custom scripts or reports.
Security extensions
Custom security extensions need some modification to work with the new web portal. Security extensions need to use the IAuthenticationExtension2 interface.
WMI Provider
The web portal application name changes from "ReportManager" to "ReportServerWebApp".