Cannot retrieve KRB5CCNAME if logged in with kerberos ticket

Quick-n-easy question: I have my apache virtual host configured to use kerberos authentication: <Location /> AuthType KerberosV5 KrbAuthRealms DOMAIN.COM KrbServiceName HTTP Krb5Keytab /etc/apache2/krb5.keytab KrbMethodNegotiate on KrbMethodK5Passwd on KrbAuthoritative off KrbSaveCredentials on Require valid-user </Location> And then I created the following test page: <html> <head> <title>PHP Test</title> </head> <body> <h1>PHP Kerberos Test</h1> <?php echo "user = {$_SERVER['PHP_AUTH_USER']}<br/>"; echo "REMOTE_USER={$_SERVER['REMOTE_USER']}<br/>"; putenv("KRB5CCNAME={$_SERVER['KRB5CCNAME']}"); echo "KRB5CCNAME={$_SERVER['KRB5CCNAME']}<br/>"; exit(); ?> </body> </html> And I have mod_auth_kerb php5 modules enabled in apache. When I try to connect to the above test page using a kerberos ticket, I do see the PHP_AUTH_USER and REMOTE_USER (which are the same). But I get nothing in KRB5CCNAME. Now, if I destory my kerberos ticket and login using kerberos user/pw, At first I do get the filename associated with KRB5CCNAME. But, if I wait less than 15s to refresh the page, I get nothing for KRB5CCNAME; if I wait more than 15s, I will get the filename for KRB5CCNAME. Does anyone know what I may be doing wrong?