Configuring the credential cache timeout
You want to configure the credential cache timeout
You can set the length of time that credentials received from the server are cached (ie. how frequently the authentication box appears). Credentials can be cached for up to 3932100 seconds. The default cache duration is 900 seconds (15 minutes). This is configured separately for each type of realm (LDAP, NTLM, Radius, etc.).
From the Management Console, go to Configuration > Authentication. The length of time to cache credentials can be set using the "Cache Credentials" setting on the following tabs: