How to sign out from HTTPS session

Hi

Suppose I have a web site with different access levels, with files
lying in different directories with there own .htpasswd files. The web
pages uses the $REMOTE_USER variable so content on higher access
levels is not shown or linked to.

How can I let the user sign out, so she can login again, possibly on
another access level? I.e. is there any standard way to tell the web
browser to renew the user/password pair?

Regards,
Z