ERROR cannot specify both legacy proxy values and juju proxy values

I'm trying a deploy behind a proxy, and I need for all services to honor that proxy setting: juju itself, the charms, apt, even snaps.

Looking at juju bootstrap --help | proxy, I see a ton of proxy settings:

apt-ftp-proxy:
apt-http-proxy:
apt-https-proxy:
apt-no-proxy:
ftp-proxy:
http-proxy:
https-proxy:
juju-ftp-proxy:
juju-http-proxy:
juju-https-proxy:
juju-no-proxy:
no-proxy:
snap-http-proxy:
snap-https-proxy:
snap-store-proxy:

So I create a config.yaml file with this:
apt-http-proxy: "http://10.96.0.10:8000/"
apt-https-proxy: "http://10.96.0.10:8000/"
apt-no-proxy: "127.0.0.1,localdomain,.localdomain,scapestack,.scapestack,10.96.0.10,10.96.0.1,squid.internal,.internal,internal"

juju-http-proxy: "http://10.96.0.10:8000/"
juju-https-proxy: "http://10.96.0.10:8000/"
juju-no-proxy: "127.0.0.1,localdomain,.localdomain,scapestack,.scapestack,10.96.0.10,10.96.0.1,squid.internal,.internal,internal"

http-proxy: "http://10.96.0.10:8000/"
https-proxy: "http://10.96.0.10:8000/"
no-proxy: "127.0.0.1,localdomain,.localdomain,scapestack,.scapestack,10.96.0.10,10.96.0.1,squid.internal,.internal,internal"

snap-http-proxy: "http://10.96.0.10:8000/"
snap-https-proxy: "http://10.96.0.10:8000/"

When I bootstrap with that, however, juju complains that I'm mixing juju proxy settings with legacy settings:
$ juju bootstrap maas --config juju-bootstrap-config.yaml --to mino.scapestack
ERROR cannot specify both legacy proxy values and juju proxy values

But it doesn't tell me which ones are the legacy ones. The bootstrap --help command doesn't have the word "legacy" in its output.