You need to store this in config, something like config :livebook, :force_ssl, true | false. And then, you need a plug in the endpoint.ex like this:

plug :force_ssl

@plug_ssl Plug.SSL.init([])
def force_ssl(conn, _opts) do
  if Application.get_env(:livebook, :force_ssl, false) do
    conn
  else
    Plug.SSL.call(conn, @plug_ssl)
  end
end

There are probably other details, but this is the minimum required to get started!

I actually think we should call the option LIVEBOOK_FORCE_SSL_HOST and it should be set to a binary which is the host we redirect to!

I actually think we should call the option LIVEBOOK_FORCE_SSL_HOST and it should be set to a binary which is the host we redirect to!

OK, I'll create new PR about this soon.
I truly appreciate your comments :)

I also think you can do something like this:

@plug_ssl Plug.SSL.init(host: {Application, :get_env, [:livebook, :force_ssl_host, nil]})

And then skip the init call here. The module attribute approach is likely more efficient, even if it has to look up the host twice.

What should I do with :force_ssl?

It is no longer used as we renamed it to force_ssl_host. :)

I got it!

Sorry, maybe there was some confusion. We don't need LIVEBOOK_FORCE_SSL anymore, only LIVEBOOK_FORCE_SSL_HOST. :)

I've solved it.