I override in the router

    sign_in_route(
      register_path: "/register",
      reset_path: "/reset",
      overrides: [
        App.Auth.Overrides,
        AshAuthentication.Phoenix.Overrides.Default
      ],
      on_mount: [{AppWeb.LiveUserAuth, :live_no_user}]
    )

App.Auth.Overrides contains my overrides, if the definition isn’t there it falls back to Default

This is what Overrides looks like:

defmodule App.Auth.Overrides do
  use AshAuthentication.Phoenix.Overrides
  alias AshAuthentication.Phoenix.{Components, ResetLive, SignInLive}

  override SignInLive do
    set :root_class, "grid h-screen place-items-center bg-brand dark:bg-brand"
  end

  override ResetLive do
    set :root_class, "grid h-screen place-items-center dark:bg-gray-900"
  end

  override Components.Reset do
    set :root_class, """
    flex-1 flex flex-col justify-center py-12 px-4 sm:px-6 lg:flex-none
    lg:px-20 xl:px-24
    """

    set :strategy_class, "mx-auth w-full max-w-sm lg:w-96"
  end

  override Components.Reset.Form do
    set :root_class, nil

    set :label_class,
        "mt-2 mb-4 text-2xl tracking-tight font-bold text-gray-900 dark:text-gray-900"

    set :form_class, nil
    set :spacer_class, "py-1"
    set :disable_button_text, "Changing password ..."
  end

  override Components.SignIn do
    set :root_class, """
    flex-1 flex flex-col justify-center py-12 px-4 sm:px-6 lg:flex-none
    lg:px-20 xl:px-24
    """

    set :strategy_class, "mx-auth w-full max-w-sm lg:w-96"

    set :authentication_error_container_class, "text-black dark:text-black text-center"
    set :authentication_error_text_class, ""
  end

  override Components.Banner do
    set :root_class, "w-full flex justify-center py-2"
    set :href_class, nil
    set :href_url, "/"
    set :image_class, "block dark:hidden h-12 w-auto sm:h-14"
    set :dark_image_class, "hidden dark:block h-12 w-auto sm:h-14"

    set :image_url,
        "https://static.wixstatic.com/media/62aad1_b2a9245d61f34d33b0228a94fdac9b8d~mv2.png/v1/fill/w_114,h_114,al_c,q_85,usm_0.66_1.00_0.01,enc_auto/white.png"

    set :dark_image_url,
        "https://static.wixstatic.com/media/62aad1_b2a9245d61f34d33b0228a94fdac9b8d~mv2.png/v1/fill/w_114,h_114,al_c,q_85,usm_0.66_1.00_0.01,enc_auto/white.png"

    set :text_class, nil
    set :text, nil
  end

  override Components.HorizontalRule do
    set :root_class, "relative my-2"
    set :hr_outer_class, "absolute inset-0 flex items-center"
    set :hr_inner_class, "w-full border-t border-gray-300 dark:border-gray-700"
    set :text_outer_class, "relative flex justify-center text-sm"

    set :text_inner_class,
        "px-2 bg-white text-gray-400 font-medium dark:bg-gray-900 dark:text-gray-500"

    set :text, "or"
  end

  override Components.MagicLink do
    set :root_class, "mt-4 mb-4"

    set :label_class,
        "mt-2 mb-4 text-2xl tracking-tight font-bold text-gray-900 dark:text-gray-900"

    set :form_class, nil

    set :request_flash_text,
        "If this user exists in our database you will contacted with a sign-in link shortly."

    set :disable_button_text, "Requesting ..."
  end

  override Components.Password do
    set :root_class, "mt-4 mb-4"
    set :interstitial_class, "flex flex-row justify-between content-between text-sm font-medium"
    set :toggler_class, "flex-none text-zinc-100 hover:text-zinc-200 px-2 first:pl-0 last:pr-0"
    set :sign_in_toggle_text, "Already have an account?"
    set :register_toggle_text, "Need an account?"
    set :reset_toggle_text, "Forgot your password?"
    set :show_first, :sign_in
    set :hide_class, "hidden"
  end

  override Components.Password.SignInForm do
    set :root_class, nil
    set :label_class, "mt-2 mb-4 text-2xl tracking-tight font-bold text-gray-900 dark:text-white"
    set :form_class, nil
    set :slot_class, "my-4"
    set :disable_button_text, "Signing in ..."
  end

  override Components.Password.RegisterForm do
    set :root_class, nil
    set :label_class, "mt-2 mb-4 text-2xl tracking-tight font-bold text-gray-900 dark:text-white"
    set :form_class, nil
    set :slot_class, "my-4"
    set :disable_button_text, "Registering ..."
  end

  override Components.Password.ResetForm do
    set :root_class, nil
    set :label_class, "mt-2 mb-4 text-2xl tracking-tight font-bold text-gray-900 dark:text-white"
    set :form_class, nil
    set :slot_class, "my-4"

    set :reset_flash_text,
        "If this user exists in our system, you will be contacted with reset instructions shortly."

    set :disable_button_text, "Requesting ..."
  end

  override Components.Password.Input do
    set :field_class, "mt-2 mb-2 dark:text-white"
    set :label_class, "block text-sm font-medium text-white mb-1 dark:text-white"

    set :input_class, """
    appearance-none block w-full px-3 py-4 border border-gray-300 rounded-md
    shadow-sm placeholder-gray-400 focus:outline-none focus:ring-slate-pale-500
    focus:border-slate-pale-500 text-lg font-medium
    text-slate-950
    dark:text-slate-950
    """

    set :input_class_with_error, """
    appearance-none block w-full px-3 py-2 border border-gray-300 rounded-md
    shadow-sm placeholder-gray-400 focus:outline-none border-red-400 sm:text-sm
    dark:text-black
    """

    set :submit_class, """
    w-full flex justify-center py-2 px-4 border border-transparent rounded-md
    shadow-sm text-md font-semibold text-white bg-slate-600 hover:bg-slate-700
    focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-slate-300
    mt-4 mb-4
    """

    set :error_ul, "text-red-400 font-light my-3 italic text-sm"
    set :error_li, nil
    set :input_debounce, 350
  end

  override Components.OAuth2 do
    set :root_class, "w-full mt-2 mb-4"

    set :link_class, """
    w-full flex justify-center py-2 px-4 border border-transparent rounded-md
    shadow-sm text-sm font-medium text-black bg-gray-200 hover:bg-gray-300
    focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-slate-600
    inline-flex items-center
    """

    set :icon_class, "-ml-0.4 mr-2 h-4 w-4"
  end
end

I think I just copied the defaults file found here and started editing in my override file: ash_authentication_phoenix/lib/ash_authentication_phoenix/overrides/default.ex at main · team-alembic/ash_authentication_phoenix · GitHub