Symptoms
If you implement the custom security extensions and configure to use forms authentication in Microsoft SQL Server 2016 Reporting Services (SSRS 2016), you will find that the Report Server web portal URL is working fine. However, the Report Server Web service URL is getting truncated with a dropped query string when it redirects to the authentication page for unauthenticated users which makes the user authentication to fail.
Resolution
This issue is fixed in the following cumulative update for SQL Server: Cumulative Update 2 for SQL Server 2016 SP1
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server:
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminologythat Microsoft uses to describe software updates.
