Mostly as a reminder to myself when I'm looking to solve this kind of problem the next time: Since the March 22, 2017 version of the FortiClient VPN Android app kept crashing on my mobile (still running the last Cyanogenmod 13 snapshot) as soon as I tried to switch away to the launcher, I wanted to downgrade the app.
Unfortunately, there's no copy on apkmirror.com or F-Droid, and I don't know about any other reasonably trustworthy sources. I also already had removed and reinstalled the app, so recovering the old version on the phone didn't seem an option either.
Fortunately, I take TWRP backups now and then, so I tried looking at one of those. For once, having unencrypted backups turned out real convenient: A TWRP data.ext4.win file is just a tar.gz, so I was able recover the app/com.fortinet.forticlient_vpn-1/base.apk file (using 7Zip on Windows), and copy that over to my phone. After uninstalling the current version of the FortiClient app, I just reinstalled the program with the CM file manager using the restored base.apk as a source. Done.
Unfortunately, there's no copy on apkmirror.com or F-Droid, and I don't know about any other reasonably trustworthy sources. I also already had removed and reinstalled the app, so recovering the old version on the phone didn't seem an option either.
Fortunately, I take TWRP backups now and then, so I tried looking at one of those. For once, having unencrypted backups turned out real convenient: A TWRP data.ext4.win file is just a tar.gz, so I was able recover the app/com.fortinet.forticlient_vpn-1/base.apk file (using 7Zip on Windows), and copy that over to my phone. After uninstalling the current version of the FortiClient app, I just reinstalled the program with the CM file manager using the restored base.apk as a source. Done.
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