Altering identity

[Marek Des]

What's the recommended way to achieve this?

I need to alter outer and inner identity:
- if outer identity is empty then alter it to "anon at domain.tld"
- if a domain is missing in inner identity then add it (so username will
become username at domain.tld)

I already tried this for outer identity:

operator_name = "domain.tld"

 authorize {
                linelog_recv_request

                split_username_nai
                if (noop || !&Stripped-User-Domain) {
                        #reject
                        update request {
                            Stripped-User-Domain := "${operator_name}"
                            Stripped-User-Name := "anon"
                        }
 }

I am getting  ERROR: EAP-Identity Unknown.