Google Cloud Identity - Terraform - Create a group that allows outside organization members

How can I create a group on Google Cloud Identity using Terraform that allows outside organization members?

I created a group using a code similar to this:

resource "google_cloud_identity_group" "team" {
  provider = google.cloud-identity

  display_name         = "team-example"
  parent               = "customers/xyz"
  description          = "Team Description"
  initial_group_config = "EMPTY"

  group_key {
    id = "team-example@example.com"
  }

  labels = {
    "cloudidentity.googleapis.com/groups.discussion_forum" = ""
  }
}

Once I tried to add a member which email belongs to another organization, I got the error below:

Error creating GroupMembership: googleapi: Error 400: Error(4023): Cannot create membership in group 'groups/xyz' for member 'person@otherdomain.com' because the group does not allow members outside the organization

I couldn't find an answer on the documentation and I even tried to find the "allow members from outside the organization" flag at the group api.

As a work-around, I need to:

create a group
access the admin.google.com
enable this flag manually

Solution

Controlling allowExternalMembers is managed via the Google Groups Settings API (https://developers.google.com/admin-sdk/groups-settings/v1/reference/groups), which is not covered by Google's terraform provider yet.

So an execution block that executes that API request might be needed here until then.