You can use ipatool to download ipa files from appstore.
Requirements
macOS 10.11 or later.
Apple ID set up to use the App Store.
github: https://github.com/majd/ipatool
install ipatool on mac:
brew tap majd/repo
brew install ipatool
first you need to login:
ipatool auth login
then you need to purchase a bundle to be able to download it:
ipatool purchase -b com.cisco.anyconnect
then you can download the bundle:
ipatool download -b com.cisco.anyconnect