I've done it this way:
I believe you can't do this on Layout level, but would need to do this on the individual pages. By making use of snippets you could minimise the amount of places you'd need to do this.
Depending on how your application is built, there are probably multiple ways to achieve showing the current user. One them I use often is by using the Microflow Label. With it, you can perform microflow actions and output a string that is displayed where you place the widget.
Create a new project using the ap cloud template it's in there. You will have a working example.
If you download the Company Expenses app, you will see an example of how to do this. As you are in version 5.13.1, you will need to navigate to the All Versions tab and download the prior version as the current version is for Modeler 5.15.