Sets the user interface (UI) customization information for a user pool's built-in app UI.

You can specify app UI customization settings for a single client (with a specific clientId) or for all clients (by setting the clientId to ALL). If you specify ALL, the default configuration is used for every client that has no previously set UI customization. If you specify UI customization settings for a particular client, it will no longer return to the ALL configuration.

To use this API, your user pool must have a domain associated with it. Otherwise, there is no place to host the app's pages, and the service will throw an error.