autoinstall fully offline iso with ubuntu jammy live ISO

I am trying a jammy live iso customization, and when I boot the ISO, installer crashes!

Specifically, subiquity/Install/install/configure_apt/cmd-in-target errors out andthe reason being apt-get update failure.

apt-get update errors out due to GPG key (NO_PUBKEY XYZ...)

So, I tried adding the following autoinstall config:

  apt:    conf: | # APT config      APT {        Get {          AllowUnauthenticated "true";        };      };

But this does not seem to be taking effect!

The syntax seems to be correct and I picked this up from curtin examples.Isn't there no equivalent of apt's --allow-unauthenticated that Ican pass to the autoinstaller/curtin?