A build issue popped up in dotnet/dotnet-buildtools-prereqs-docker#683 which was getting a failure when attempting to run the build-rootfs.sh script. It was failing due to an expired cert for pkgsrc.joyent.com. The build-rootfs.sh script currently references the pkgsrc.joyent.com domain:

However, according to this SmartOS announcement, the recommendation is to migrate off of this domain. The script should be updated accordingly.