Could you maybe, first then download the file to Omnia it self.
using
wget https://github.com/k-szuster/luci-access-control/releases/download/v0.3.1/luci-app-access-control_0.3.1_all.ipk
Then
opkg install luci-app-access-control_0.3.1_all.ipk
If it worked, then later on, remove the luci-app-access-control_0.3.1_all.ipk file
with
rm luci-app-access-control_0.3.1_all.ipk
remember this will only delete the file ipk, not remove the installation that just took place.
Off course you could also, keep the ipk file if you wish, that is up to you. It is comparable like a *.exe file on windows or *.deb file on a debian-ish related linux distro.
Let me know if it worked.