IDCS introspect REST API must return username of person requested access in sub field

Summary:

Hi Team

I'm making use of introspect REST API to get the username of person who has got the access token to validate the access, but in introspect REST API response in sub i could see only client id information instead of username, no where i see the email address of person who has generated access token.

Can you please let me know when we use /oauth2/v1/token REST API what details we may need to pass so that in introspect response we can get the email address or username of person who has generated the token. also, what needs to be used while configuring confidential application