How Do I Set Remote_User in a Http Header?

I've got an issue with my Apache settings.

I installed a web application that partly accepts external authentication:

• I use Apache to manage the access to my application web pages.
• If the authentication is successful, the environment variable REMOTE_USER is set with the user's name.
• Then the user name is passed to my application through the HTTP header so the application opens on the user session.
• This is mostly an Apache configuration for the application. I only set the name of the variable (HTTP header) that contains the username in my application config file.

Here is the issue : I can authenticate successfully (most of the time) but my HTTP header is set to null.

Some additional details :

• I use Apache and the mod_perl modules (AuthenNIS + AuthzNIS + Net-NIS) to authenticate to my app with NIS account.

• With the following Apache config file I have the authentication form when I try to access my application but the REMOTE_USER header is set to null.

      Listen 2208
      <VirtualHost *:2208>
  
                  RewriteEngine on
                  DocumentRoot "/path/to/static"
  
  
                  <Directory "/path/to/static">
  
                              Options +Indexes FollowSymLinks MultiViews
                              AllowOverride None
                              Order allow,deny
                              Allow from all
  
  
                              AuthType Basic
                              AuthName "Authentifiez vous"
                              PerlAuthenHandler Apache2::AuthenNIS
                              PerlAuthzHandler Apache2::AuthzNIS
                              PerlSetVar AllowAlternateAuth no
                              require valid-user
  
                  </Directory>
  
  
                  RewriteEngine on
                  RewriteRule . - [E=RU:%{LA-U:REMOTE_USER}]
                  RequestHeader set REMOTE_USER %{RU}e
  
                         RewriteRule ^/apps$ /apps/ [R]
                         RewriteRule ^/static/style/(.*) /path/to/static/june_2007_style/blue/$1 [L]
                         RewriteRule ^/static/scripts/(.*) /path/to/static/scripts/packed/$1 [L]
                         RewriteRule ^/static/(.*) /path/to/static/$1 [L]
                         RewriteRule ^/favicon.ico /path/to/static/favicon.ico [L]
                         RewriteRule ^/robots.txt /path/to/static/robots.txt [L]
                         RewriteRule ^(.*)  [P]
  
      </VirtualHost>
  

If I set RequestHeader set REMOTE_USER "username" the application opens on the corresponding user session.

To see the value of REMOTE_USER I use the Firebug Firefox module to display the values of the http header + my application has a script that displays the value of variables passed to it.

I tested an almost identical Apache configuration on an index.php page that displays the values of server variables in a http request. The difference lies in the RewriteRules.

        <?PHP
                    foreach($_SERVER as $key_name => $key_value) {
                    print $key_name . " = " . $key_value . "<br>";

                    }
        ?>

In this case, I get a REMOTE_USER et HTTP_REMOTE_USER with a username value.

I don't understand where my problem lies.

Apache 2.2.31 RedHat 6.5

Thanks in advance !