Pass variable through policy using iRule

https://example.com/consume.aspx is the AssertionConsumerService but is also the app/relying party. The app then logs the user in unless contentid exists, in which case it should forward directly to that contentid (usually a document or video) without completely logging them in (but this occurs in the target application). The tricky part is getting the value into the response assertion if the custom session variable is set in an iRule. If I were to use a cookie would this work?:

when RULE_INIT {
    set cookie_name "contentid"
}
when ACCESS_SESSION_STARTED { 
    set c_id [HTTP::query]

    if { $c_id ne "" } {
        HTTP::cookie insert name $::cookie_name value $c_id
    } else {
        HTTP::cookie remove $::cookie_name
    }   
}