API authorization doesn't work on staging

When trying to follow the instructions on https://help.launchpad.net/API/launchpadlib, I get this error.

>>> launchpad = Launchpad.get_token_and_login('just testing', STAGING_SERVICE_ROOT, cachedir)
The authorization page (https://staging.launchpad.net/+authorize-token?oauth_token=VsHF1WntvMXcn76bcBXl) should be opening in your browser. After you have authorized this program to access Launchpad on your behalf you should come back here and press <Enter> to finish the authentication process.

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "launchpadlib/launchpad.py", line 155, in get_token_and_login
    return cls(credentials, service_root, cache, timeout, proxy_info)
  File "launchpadlib/launchpad.py", line 60, in __init__
    self._wadl = self._browser.get_wadl_application(self._root_uri)
  File "launchpadlib/_browser.py", line 229, in get_wadl_application
    url, media_type='application/vd.sun.wadl+xml')
  File "launchpadlib/_browser.py", line 211, in _request
    raise HTTPError(response, content)
launchpadlib.errors.HTTPError: HTTP Error 401: Unauthorized

I asked leonardr about this on IRC, and it seems that this is a known issue: authentication doesn't work with staging.