Switch from passing through **kw to just auth=...
Switch from passing through **kw to just auth=...

After discussion with Bryce, passing through all kwargs breaks our independence
from requests, and makes it less clear what we've tested and know to work. To
limit/control usage, replacing this with an explicit addition of the auth=...
kwarg that the NexusClient needs.

globus/globus-sdk-python,globus/globus-sdk-python,sirosen/globus-sdk-python,globusonline/globus-sdk-python,aaschaer/globus-sdk-python