How to write an App with dynamic compose to mount/umount as needed?

[kratsg]

It seems if one tries to do something reactive like below

from textual.app import App, ComposeResult
from textual.containers import Container, Horizontal, Vertical
from textual.reactive import reactive
from textual.widgets import Button, Footer, Header

class LoginForm(Container):
    def compose(self) -> ComposeResult:
        yield Vertical(
           Button("Login", id="login", variant="primary")
        )   

    def on_button_pressed(self, event: Button.Pressed) -> None:
            self.app.show_login = False


class Browser(App):
    show_login = reactive(False)

    def compose(self) -> ComposeResult:
        """Call to compose the app"""
        yield Header()
        yield Footer()
        if self.show_login:
            yield LoginForm()
            self.set_focus(None)
        else:
            yield Horizontal(
                CustomContainerSlowToLoadRequiresLogin()
            )
            self.set_focus(self.institution_list)

It doesn't seem like self.app.show_login=False will trigger compose() to re-run. I might be thinking about this wrong, and while Screen is an option here, it doesn't give me the right functionality I'm looking for because CustomContainerSlowToLoadRequiresLogin is going to need a valid access token that comes from the LoginForm (e.g. username/password) before it can run. The way I set this up is to have CustomContainerSlowToLoadRequiresLogin do something with the access token on_mount because it only needs to run once to initialize its data, and doesn't need to make anymore API calls after that.

Is there something in Textual that allows this design pattern, or how can I rework my logic to make it work?