In the documentation for Centrify Report Services, it mentions setting up permissions in SSRS for user accounts that need to access Report Services to view (Report Viewer) and write (Report Writer) reports. 

This article goes over the section for "Required SSRS permissions" (Report Admin, Report Viewer, Report Writer) in below table from the documentation.

https://docs.centrify.com/en/css/2017.3-html/index.html#page/Reporting%2FBefore_installing_-_prerequisites.2.html%23ww1044578

In order to set permissions for SSRS, you need to be logged into the Report Server with your Report Admin or the installer/administrator account used to install and configure Centrify Report Service. 

Site Settings is in the top right corner of the browser.

In Site Settings, Click on Security and then New Role Assignment

Add the user or group using the following syntax: \ or \

Then check the desired Role for the user or group from the selections below.

Click Ok.

Folder Settings is also found on the initial page after logging into Centrify Report Services.

In Folder Settings -> Click on "Security" -> Click on "New Role Assignment"

In the "New Role Assignment", Add the user or group using the following syntax: \ or \

Then check the desired Role for the user or group in the sections below.

Click Ok.

Centrify documentation:
https://docs.centrify.com/en/css/2017.3-html/index.html#page/Reporting%2FConfiguring_SQL_Server_Reporting_Services_(SSRS).8.html%23ww1052268

See following link as a reference:

https://docs.microsoft.com/en-us/sql/reporting-services/security/grant-user-access-to-a-report-server