Ok, did a proof of concept.

Global hook at app.html.heex

<main id="main" phx-hook="MainHook" class="px-4 py-20 sm:px-6 lg:px-8">
  <div class="mx-auto max-w-2xl">
    <.flash_group flash={@flash} />
    <%= @inner_content %>
  </div>
</main>

The hook

Hooks.MainHook = {
    mounted() {
        let token = localStorage.getItem("uuid")
        if(token == null) {
            // here you should push an event to the server and fetch a
            // tamper proof token and save it to localStorage and
            // all other security considerations
            token = "1234"
        }
        this.pushEvent("subscribe_to_channel", {uuid: token})
    }
}

The module attaching the server hooks

defmodule ExampleWeb.MultipleTabs do
  import Phoenix.LiveView

  def on_mount(:default, _params, _session, socket) do
    {:cont,
     socket
     |> attach_hook(
       "subscribe_to_channel",
       :handle_event,
       &subscribe_to_channel/3
     )
     |> attach_hook(:handle_reload, :handle_info, &reload_page/2)}
  end

  defp reload_page(_msg, socket) do
    # Here you'll need to figure out a way to get the url
    # to redirect to the correct place
    {:cont, socket |> redirect(to: "/")}
  end

  defp subscribe_to_channel("subscribe_to_channel", %{"uuid" => uuid}, socket) do
    # Here you should validate the token before subscribing
    Phoenix.PubSub.subscribe(Example.PubSub, "reload##{uuid}")
    {:cont, socket}
  end
end

And then just put it in a live session in the router

    live_session :default, on_mount: ExampleWeb.MultipleTabs do
      live "/", HomeLive
    end

Then you can call Phoenix.PubSub.broadcast(Example.PubSub, "reload#1234", []) from anywhere and all pages will redirect to /.

Security considerations aside it is pretty simple.

You’ve implemented phx.gen.auth so you’re probably aware of the LiveView disconnect when the user logs out. That forces the tabs to reload.

If you come up with a way to identify all the tabs which belongs to the same guest user (ip?, browser fingerprint?, setting an identifier in the session at first page load and using it afterwards [like a fake user id]?) and set the live_socket_id accordingly, you can also disconnect all the “guest” LiveViews to force a page reload that will fetch the newly signed in user.

My naive first approach would be something like:

1. At any new tab check if there’s a token (preferably tamper proof) in local storage and send it to the server, if not, ask for one from the server with an unique identifiable payload (maybe an UUID) and save it in the local storage, in this case only the first page load will actually create a token.

2. Using on_mount use attach_hook/4 to handle the pushed event with the uuid to subscribe to a “guest#{uuid}” channel and the incoming handle_info/2 messages from pubsub.

3. When the user successfully log in you can broadcast a message to the guest#{uuid} channel that will be handled by the handle_info/2 callback of all liveviews subscribed to that channel.

Security considerations aside (short lived tokens, single use, yadda, yadda, yadda) I think someone could build it in a couple hours.

A bit more javascript than I like to write though…