[doc issue] insufficient explanation of an app router's xs-security-json

[bauer-at-work]

Issue description

To get the user attributes from the custom IdP, add the following property to xs-security.json file of the application router:

Out of the box, the xs-security.json file does not exist for a CAP project.
It is not created automatically upon running cds add approuter.
The xs-security.json is not listed either as an app router resource file:
https://help.sap.com/docs/btp/sap-business-technology-platform/resource-files

For all those reasons, I am unable to tell what a default xs-security.json for ann app router should look like.

Feedback Type (Optional)

content gaps

Page Title on SAP Help Portal (prefilled)

User API Service

Page URL on SAP Help Portal (prefilled)

https://help.sap.com/docs/btp/sap-business-technology-platform/user-api-service?locale=en-US&advPhr=xs-security.json