Cookies: Making them last longer than a session
This will enable users to remain logged in beyond one browser session.
If a Plone instance is being used as an intranet, repetitive logging in is a barrier to ease-of-use. This can also apply to internet sites. This can be circumvented by allowing the user to remain logged in after they close their browser.
Setting cookie expiration length:
- Call up the ZMI via http://your_portal_url/manage
- Go to portal_properties
- Choose site_properties
- Alter auth_cookie_length to the number of days you wish to let your users stay logged in for.
That's it. Easy when you know how.

plone 3