Creating an Identity referencing a key within a :map attribute (postgres-stored jsonb)

 attributes do
    uuid_primary_key :id

    attribute :source, :atom do
      constraints one_of: [:source_one, :source_two]
    end

    attribute :original_json, :map
  end

identities do
  
  #something like this?
  identity :synthetic_id [:source, :original_json["Key"]]

end