I think you can find it here. But I don't remember if I got the information here. I think somewhere in a community thread:
Contains a string corresponding to a Qlik Sense SaaS user name. Qlik Sense SaaS will get the login information from the IdP subject and compare it to the value in this field. For an alternate way to verify user identity using email address, see USER.EMAIL. For multi-cloud environments, the IdP subject can be mapped against your internal Windows identity . When using Qlik Account, the subject cannot be mapped against internal Windows identity. User IdP subject can be viewed in the Users section of the Management Console.