auth_controller.ex

defp authenticate(%{info: info, uid: uid}) do
  email = Map.get(info, :email)
  name = Developer.format_username(Map.get(info, :name))

  case String.match?(email, ~r/@your_domain.com$/) do  #  Change your_domain to your domain
    true ->
      attrs = %{
        email: email,
        username: name,
        google_id: uid
      }

      Developer.find_or_create(Repo, attrs)

    _ ->
      {:error, email}
  end
end