a secure of phoenix Plug.Session set value on runtime

I want to set value of secure on runtime. But it is set value on compile time. I don’t know how to do that. My env is elixir 12, erlang 24 Plz help me

plug Plug.Session, store: :cookie, key: "_key", signing_salt: "KahwH24", max_age: 60 * 60, secure: System.get_env("PLUG_SESSION_SECURE", "true") == "true"