Need to allow request only if application opens from parent portal

Formatted example :

on VIP1 :

when HTTP_RESPONSE {
    if { [HTTP::cookie exists "MySessionCookie"] } {
        HTTP::cookie domain "MySessionCookie" "example.com"
    }
}

on VIP2 :

when HTTP_REQUEST {
    if { ([HTTP::cookie exists "MySessionCookie"]) } {
         insert code to add cookie validation
    } else {
        HTTP::redirect "https://vip1.example.com/login"
    }
}

But clearly, it would be easier to use APM module and put an access profile with multi-domain sso on both VIP and configure Web SSO for VIP1.