Kerberos Authentication : REDIRECT_REMOTE_USER is disappearing

Question

I am trying the Kerberos Authentication for my Drupal site. I got the REDIRECT_REMOTE_USER from the $_SERVER variable. But after getting its value for the first time, it disappeared from the $_SERVER variable.

my config is

/etc/apache2/sites-available/000-default.conf:

<VirtualHost *:80>
     
        ServerAdmin serveradminValue
        DocumentRoot /var/www/html
        ServerName ${SERVER_HOST_NAME}

        LogLevel info auth_gssapi:debug

        <IfModule !mod_auth_gssapi.c>
          LoadModule auth_gssapi_module /usr/lib64/httpd/modules/mod_auth_gssapi.so
        </IfModule>

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

        <Location /sso>

         AuthType GSSAPI
         AuthName "GSS Auth"
         GssapiAllowedMech krb5
         GssapiCredStore keytab:/var/www/keytab/myKeyTab.keytab
         GssapiNegotiateOnce Off
         GssapiBasicAuth Off
         GssapiLocalName On
         BrowserMatch Windows gssapi-no-negotiate
         GSSapiImpersonate Off
         GssapiSSLonly Off
         Require valid-user

       </Location>

</VirtualHost>

Can anyone please help me about this?