Overview of SQL Server Reporting Services 2012 Architecture, Features, and Tools - Learning SQL Server Reporting Services 2012 - page 161

Custom (Anonymous) No Anonymous authentication

directs the Report Server to
ignore the authentication
header in an HTTP request.
The Report Server accepts
all requests, but call on, a
custom ASP.NET Forms
authentication that you
provide to authenticate the
user.
Specify custom only if you
are deploying a custom
authentication module that
handles all authentication
requests on the Report
Server. You cannot use the
custom authentication type
with the default Windows
Authentication extension.

For the Report Server Kailua used in this topic, the authentication is as shown in the
following XML block in the rsreportserver.config file described earlier.

Please review this in the configuration files
in the <Authentication/> node.

Authentication types such as Anonymous, Passport, Digest, and so on are
not supported.

Basically, the Report Server uses the authentication provider and permissions
defined in the SharePoint Web Application to control access to Report Server items.
SharePoint authentication can be Windows authentication or Forms authentication.
The assignment of roles follows a similar pattern to Native mode but the number of
tasks a role can perform is lot more fine-grained than a Native mode installation.

In the present case where the computer administrator installed the SharePoint Server
and configured the portal site, he is the site owner. The administrator in this case set
permissions to the SharePoint Web Application as we shall see later.