"You cannot use a custom login page with Identifier First"

Problem statement

On the Authentication profile page, the following warning is shown when trying to select Identifier First:

You cannot use a custom login page with Identifier First


This message indicates that the ‘Customize Login Page’ (found under the Advanced options) is enabled. When enabled, the login page uses the classic experience instead (despite new being selected) and allows full HTML customisation. This ignores the Authentication profile selected since the behavior is now determined by the custom page.

To use the new experience with only the standard customization options (vs. an entirely customized page), turn off the option by going to:

  1. Navigate to Branding > Universal login.
  2. Then click on Advanced options > Login tab.
  3. Turn off the Customize Login Page toggle.

Once it is turned off, it is then possible to use Identifier First, as the new universal login page is now in use rather than the fully customized page.