Login with external user can end up with the wrong whoami

[Simon Richardson]

Login via @external can result in the wrong information being written to the local accounts.yaml. This can be confusing, as it _can_ be perceived that you're acting on the behalf of someone else. Although, as soon as you attempt to talk to the controller, the accounts.yaml is updated with the right information and whomai reports the right information.

It can be reproduced via:

    juju bootstrap lxd test --config identity-url=https://api.jujucharms.com/identity --config allow-model-access=true
    juju grant <user>@external superuser
    juju logout
    juju login -u <user>@external
    juju whoami

[Simon Richardson (simonrichardson)]

PR https://github.com/juju/juju/pull/17667