Authentication doesn't work with CouchDB if option require_valid_user is enabled #387

require_valid_user = true

requests.exceptions.HTTPError: 401 Client Error: Unauthorized for url: http://127.0.0.1:5984/_session

diff --git a/src/cloudant/_client_session.py b/src/cloudant/_client_session.py
index 0e8fd38..d608f8e 100644
--- a/src/cloudant/_client_session.py
+++ b/src/cloudant/_client_session.py
@@ -148,6 +148,7 @@ class CookieSession(ClientSession):
             'POST',
             self._session_url,
             data={'name': self._username, 'password': self._password},
+            auth=(self._username, self._password)
         )
         resp.raise_for_status()

$ pip list | grep cloudant
cloudant (2.8.1)

$ python --version
Python 3.6.5

# This works
import requests
import json
auth = ('admin', '31sf13b3r!')
get_url = "http://127.0.0.1:5984/_session".format(auth[0])
r = requests.get(get_url, auth=auth)
print(json.dumps(r.json(), indent=1))


# This doesn't work
from cloudant import CouchDB
db = CouchDB(*auth, url='http://127.0.0.1:5984')
db.connect()
print(db.all_dbs())