Vsphere-iso configuration_parameters example?

Using the vsphere-iso builder, trying to create a template and include an attribute for build date. Looks like this can be added with configuration_parameters, and it would be an extraConfig since it’s not a default property. Trying to include that in my HCL config but it errors out every time before the template build can even start.

configuration_parameters = [
extraConfig = [
“TemplateBuildDate” = “${var.template_date}”

Error: Missing item separator
Expected a comma to mark the beginning of the next item.

Is this possible, and if so is there an example as to how it would work in this specific situation? Thanks.