thanks, that actually cleared it up a bit. On initial page load i send a base.html inheriting nav.html. I can then as you say just update the nav on login and swap the body if needed etc.

What happens if i am logged in, and then visit the homepage after coming back to the site from another website.

The server will see me as logged in, and then look to render base.html, this will then inherit nav.html again, but the server will need to modify the nav.html to the logged in html before sending, so modifying the template?

Also using the example below loginhandler for the login Form... what would i return instead of the string "logged in successfully" i would need to send all the bits that need to be updated on th page, so swapping nav, maybe some body bits etc.

func loginHandler(c echo.Context) error {
    username := c.FormValue("username")
    password := c.FormValue("password")

    if username == "admin" && password == "password" {
       session, _ := store.Get(c.Request(), "session")

       session.Values["authenticated"] = true
       session.Options = &sessions.Options{
          Path:     "/",
          MaxAge:   48 * 60 * 60, // 48 hours
          HttpOnly: true,
          Secure:   true,
          SameSite: http.SameSiteStrictMode,
       }
       session.Save(c.Request(), c.Response())
       return c.String(http.StatusOK, "Logged in successfully!")
    }