How to set the user for ReportViewer in local mode?

[Dennis McCarthy]

I am using the WebForms report viewer in local mode in an ASP.NET page. My
web application does its own authentication and access control, so Windows
Integrated Authentication is disabled and anonymous access is enabled for the
virtual directory. The report RDL uses User!UserID. This is evaluating to
the Windows user account for anonymous access. I need it to evaluate to one
of my application user accounts. I have tried setting the principal on the
current thread and on the current HTTP context, but neither affected the
value of User!UserID. I have found articles that explain how to do this with
a custom security extension in server mode reporting, but nothing on how to
do this in local mode reporting.

What must I do to make User!UserID evaluate to an application user when the
ReportViewer is running in local mode?

Thanks,
Dennis