Comment 1 for bug 1617879

There are two way we can do this, the first, and easiest, would be to delegate to charm pull to do the actual fetching for us. Otherwise we need to create a python implementation of the "bakery" authentication protocol and use that when we fetch the charm.

It should be noted that the charm pull command only (currently) supports a somewhat convoluted login mechanism based around Ubuntu SSO OAuth tokens, which might be fiddly to set up for codetree uses.