[imp] removing cookie when logging out of imp

[Scott Alexander]

Hi,

I'm creating a single sign on between IMP and our own built application. 
My single signon page is checking for the presence of the horde cookie 
with javascript. Javascript can still see the session_id in the horde 
cookie. If the horde cookie is not present then login and passwd fields 
are displayed. If it is present then user sees links to IMP and our 
extranet.

Why when a user logs out of IMP the horde cookie is not removed from the 
browser? Everything is working ok with IMP, user is logged out. I'm just 
wondering why I can still the Horde cookie's value.

I'm using horde-3.1.3 and  imp-h3-4.1.3 with mysql based sessions. 
Sessions last for 0 seconds.

My own app is using mod_perl and I'm removing the cookie using

$str = $self->cookie_string(
        request => $r,
        key     => $cookie_name,
        value   => $session_id,
        expires => 'Mon, 21-May-1971 00:00:00 GMT'
    );

Where in the horde code can I edit to do a similar thing is there a 
setting in Horde to do this?

Regards and thanks
Scott