can i access HTTP Variables in a R Shiny script?

Question

I have a CAS authenticated Apache server with redirects to shiny like this

<VirtualHost *:80>

     <Proxy *>
         Allow from localhost
     </Proxy>


     RewriteEngine on



     RewriteCond %{HTTP:Upgrade} =websocket
     RewriteRule /shiny/(.*) ws://localhost:3838/$1 [P,L]
     RewriteCond %{HTTP:Upgrade} !=websocket
     RewriteRule /shiny/(.*) http://localhost:3838/$1 [P,L]
     ProxyPass /shiny/ http://localhost:3838/
     ProxyPassReverse /shiny/ http://localhost:3838/

     ProxyPass /shiny-admin/ http://localhost:4151/
     ProxyPassReverse /shiny/ http://localhost:4151/



</VirtualHost>

what i want to do however is read and use the REMOTE_USER http variable in the shiny scripts how can I get this from the apache httpd variables????