proxy for a single user

Hello,

My internet provider is secured by an encrypted tunnel. To download e-mails
and access the internet, I have to install a proxy on my local machine
(example: konqueror: use proxy yes, proxy asas:8080 to access an http page;
asas will do the communication, the advantage is an encrypted date transfer
and no identification needed to access privat data). But there is a
problem: Once one user starts its asas-proxy (with its one certificate),
every user can access its privat stuff using the same proxy.

Is it possible to restrict the proxy-use exclusively to the user who started
the proxy?

thanks

fabio vassalli