Missing authorization in the unit resources download route in Canonical Juju 4.0 through 4.0.15...

Missing authorization in the unit resources download route in Canonical Juju 4.0 through 4.0.15 allows a controller-authenticated principal (a unit agent, or a user with only login permission) to read any application's charm resource in any model,  including container-registry credentials, via a crafted request naming an arbitrary unit.