Application Composer Server Scripts dynamic fusion url

Hi,

Does anyone know if its possible or the syntax to use to amend the following Groovy def line variable so that it automatically uses the correct Oracle Fusion host domain url. We have to update it manually after each P2T/T2T so seeing if its possible to do it without manual intervention. The script generates an email with a deeplink to the Service Request and was developed several years ago.

I was tempted to amend to use https://#{header["host"]} however one of our developers mentioned that using this syntax its no longer supported in an Expression Language which this is not.