User access to other application data

If the user is part of relevant group in other application they can have data access. So add user to the group that has viewer access to underlying record type and query rules of other application then user will be able to show the data in front end. If you dont want user to have any other access to the another app then I would suggest creating a group specific to your application users and add them as viewers to another app’s record type rather than adding user to a pre-existing group in other application.

Depending on what “show in the front end” actually means, you can use Appian groups to control access to taking actions separate from accessing data.

Access to the application (and by extension the Record Type) is the minimum to get access to the data. Record or Field Level Security can also restrict the access further.

https://docs.appian.com/suite/help/26.9/secure-your-data-fabric.html