AuthorizedSession attempts to refresh token when no refresh token was provided

[salty-horse]

Using google-auth 1.4.1

If google.auth.transport.requests.AuthorizedSession is used with an expired token, it will automatically try to refresh the token even if no refresh token was provided to the credentials object.
This causes the unreadable exception
TransportError: Invalid URL 'None': No schema supplied. Perhaps you meant http://None?

There should be a sanity check for a non-existing refresh token before any refresh attempt is made. A proper exception should be raised if the token is expired.

Sample code:

import google.oauth2.credentials
from google.auth.transport.requests import AuthorizedSession
credentials = google.oauth2.credentials.Credentials('an_expired_token')
authed_session = AuthorizedSession(credentials)
response = authed_session.get('some_url_requiring_authentication')

Traceback:

  File "/usr/lib/python3.6/site-packages/requests/sessions.py", line 521, in get
    return self.request('GET', url, **kwargs)
  File "/usr/lib/python3.6/site-packages/google/auth/transport/requests.py", line 218, in request
    self.credentials.refresh(auth_request_with_timeout)
  File "/usr/lib/python3.6/site-packages/google/oauth2/credentials.py", line 126, in refresh
    self._client_secret))
  File "/usr/lib/python3.6/site-packages/google/oauth2/_client.py", line 237, in refresh_grant
    response_data = _token_endpoint_request(request, token_uri, body)
  File "/usr/lib/python3.6/site-packages/google/oauth2/_client.py", line 106, in _token_endpoint_request
    method='POST', url=token_uri, headers=headers, body=body)
  File "/usr/lib/python3.6/site-packages/google/auth/transport/requests.py", line 124, in __call__
    six.raise_from(new_exc, caught_exc)
  File "<string>", line 3, in raise_from
google.auth.exceptions.TransportError: Invalid URL 'None': No schema supplied. Perhaps you meant http://None?

[theacodes]

Great catch! Fix incoming.