Custom gdm session logs me out on Ubuntu 18.04

I have a requirement where a sandbox user only needs to see a single application without running Gnome or any DE at all (basically a kiosk setup).

I created a new .desktop file in /usr/share/xsessions, which runs a shell script that launches and configures the application. However, shortly afterwards, the whole session is terminated (I am assuming because the batch file ends).

One of the things I tried was adding a /bin/bash at the end of it to keep it running in the background, but that doesn't help.

Looking at this question it seems that the standard way to do it is to put the application call itself into a loop. However, I can't do that because of the nature of this application. I need to launch the application first, and run other commands afterwards before surrendering control to the user.

Here is a simplified version of my script:

google-chrome &
sleep 5
xdotool search --onlyvisible --name chrome windowmove %@ 0 0
/bin/bash # ??? doesn't work

For anyone looking for this in the future, I solved it by running a loop that checks whether the main app window is still open. This solves both the issue of keeping the session alive as well as logging the user out once they close Chrome.

Replaced the last line with this and it works like a charm:

while xdotool search --onlyvisible --name chrome; do sleep 3s; done