Reflect the upstream group membership into the Supervisor's
downstream tokens, so they can be added to the user's
identity on the workload clusters.
LDAP group search is configurable on the
LDAPIdentityProvider resource.
- Bad usernames and passwords aren't really errors, since they are
based on end-user input.
- Other kinds of authentication failures are caused by bad configuration
so still treat those as errors.
- Empty usernames and passwords are already prevented by our endpoint
handler, but just to be safe make sure they cause errors inside the
authenticator too.
