Some users have numerous accounts with an identity provider. For these users, it's beneficial for the account selection UI to provide contextual information on the account beyond.

For example, users frequently have numerous Google accounts, when signing into a YouTube embed they may not remember which account they predominantly use on the YouTube service. User's would benefit from contextual signals, for example how many "channel subscriptions" they have on each Google account, or even just a "recently active on YouTube" indication.

In this case, the Identity provider (Google) could determine what account signals it will support (# channels subscribed to), and the embed app (YouTube) could specify which account signals are relevant to the given user context.