i'm trying to use the firstapp tutorial and I'm sure I'm missing something obvious. here's my code:

from libcloud.compute.types import Provider
from libcloud.compute.providers import get_driver

auth_username = 'admin'
auth_password = 'admin'
auth_url = 'http://172.16.0.2:5000/v2.0/'
project_name = 'admin'
region_name = 'RegionOne'

provider = get_driver(Provider.OPENSTACK)
conn = provider(auth_username,
                auth_password,
                ex_force_auth_url=auth_url,
                ex_force_auth_version='2.0_password',
                ex_tenant_name=project_name,
                ex_force_service_region=region_name)

flavors = conn.list_sizes()
for flavor in flavors:
    print(flavor)

The credentials should work; I've tried them manually:

nick@virtualdocs:~/pythonfirstapp$ nova --os-username=admin --os-tenant-name=admin --os-auth-url=http://172.16.0.2:5000/v2.0 list
OS Password:
+----+------+--------+------------+-------------+----------+
| ID | Name | Status | Task State | Power State | Networks |
+----+------+--------+------------+-------------+----------+
+----+------+--------+------------+-------------+----------+

And yet, when I run the python app, I'm getting an error:

Traceback (most recent call last):
  File "sample.py", line 18, in <module>
    flavors = conn.list_sizes()
  File "/usr/local/lib/python2.7/dist-packages/libcloud/compute/drivers/openstack.py", line 246, in list_sizes
    self.connection.request('/flavors/detail').object)
  File "/usr/local/lib/python2.7/dist-packages/libcloud/common/openstack.py", line 200, in request
    raw=raw)
  File "/usr/local/lib/python2.7/dist-packages/libcloud/common/base.py", line 657, in request
    action = self.morph_action_hook(action)
  File "/usr/local/lib/python2.7/dist-packages/libcloud/common/openstack.py", line 255, in morph_action_hook
    self._populate_hosts_and_request_paths()
  File "/usr/local/lib/python2.7/dist-packages/libcloud/common/openstack.py", line 288, in _populate_hosts_and_request_paths
    osa = osa.authenticate(**kwargs)  # may throw InvalidCreds
  File "/usr/local/lib/python2.7/dist-packages/libcloud/common/openstack_identity.py", line 841, in authenticate
    return self._authenticate_2_0_with_password()
  File "/usr/local/lib/python2.7/dist-packages/libcloud/common/openstack_identity.py", line 866, in _authenticate_2_0_with_password
    return self._authenticate_2_0_with_body(reqbody)
  File "/usr/local/lib/python2.7/dist-packages/libcloud/common/openstack_identity.py", line 871, in _authenticate_2_0_with_body
    method='POST')
  File "/usr/local/lib/python2.7/dist-packages/libcloud/common/base.py", line 736, in request
    response = responseCls(**kwargs)
  File "/usr/local/lib/python2.7/dist-packages/libcloud/common/base.py", line 117, in __init__
    raise Exception(self.parse_error())
Exception: {"error": {"message": "get_version_v2() got an unexpected keyword argument 'auth'", "code": 400, "title": "Bad Request"}}

I'm running this on Ubuntu 12.04 in VirtualBox, against Mirantis OpenStack 6.1. I'm sure I'm missing something obvious but for the life of me I can't see what it is.

Thanks in advance....

[UPDATE: I've since successfully connected using JClouds, so there's nothing wrong with the OpenStack install itself.]

[Second UPDATE: In response to the suggestion that I missed the "v" in the authentication URL -- thanks! -- I've updated the code and the response. Unfortunately it still doesn't work. :( ]