Icinga2: Apply service to vhosts for each host in a hostgroup

I have a series of webservers (WS1, WS2, and WS3), which belong to the HostGroup "my-web-servers".

Each of these webservers have several vhosts:

• WS1 has example1.org and example2.org.
• WS2 has example3.org, example4.org, and example5.org.
• WS3 has example6.org.

I want to apply a service to them (check_http, which will check the expiration of SSL certs) to ALL the vhosts for each of the hosts in the hostgroup.

How do I write that assign where statement?

What I have so far:

apply Serivce "SSL Certificate" for (host => value in hostgroup.hosts) {
  import "active-service-HARD-1day"
  check_command "check_ssl_cert"

  assign where host.var.vhosts
}