Confusing behavior of `login` with `make_clients=True`

[WardLT]

login will return a mix of Clients and Authorizers when you set make_clients=True. While this makes the code robust to users requesting authorizers for services that are not known by mdf_toolbox, it requires users to know what services are defined in their specific version of toolbox to know what output type(s) to expect . I suggest we throw errors instead.

Line in question:

toolbox/mdf_toolbox/auth.py

Line 205 in d6f82ff

if make_clients and scope in KNOWN_CLIENTS.keys():