Prevent churn on ccaches
    
    We slice down the received cookie so that just the content that matter
    is preserved. Thi is ok because servers can't trust anything else anyway
    and will accept a cookie with the ancillary data missing.
    
    By removing variable parts like the expiry component added by
    mod_session or the Expiration or Max-Age metadata we keep only the part
    of the cookie that changes only when a new session is generated.
    
    This way when storing the cookie we actually add a new entry in the
    ccache only when the session actually changes, and this prevents churn
    on FILE based ccaches.
    
    Related https://pagure.io/freeipa/issue/6775
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>