diff --git a/swh/lister/core/lister_transports.py b/swh/lister/core/lister_transports.py
index 01ee9f2..1bef317 100644
--- a/swh/lister/core/lister_transports.py
+++ b/swh/lister/core/lister_transports.py
@@ -1,97 +1,97 @@
 # Copyright (C) 2017 the Software Heritage developers
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import abc
 import random
 from datetime import datetime
 from email.utils import parsedate
 from pprint import pformat
 
 import requests
 import xmltodict
 
 from .abstractattribute import AbstractAttribute
 from .lister_base import FetchError
 
 
 class SWHListerHttpTransport(abc.ABC):
     """Use the Requests library for making Lister endpoint requests.
 
     To be used in conjunction with SWHListerBase or a subclass of it.
     """
 
     PATH_TEMPLATE = AbstractAttribute('string containing a python string'
                                       ' format pattern that produces the API'
                                       ' endpoint path for listing stored'
                                       ' repositories when given an index.'
                                       ' eg. "/repositories?after=%s".'
                                       'To be implemented in the API-specific'
                                       ' class inheriting this.')
 
     def request_headers(self):
         """Returns dictionary of any request headers needed by the server.
 
         MAY BE OVERRIDDEN if request headers are needed.
         """
         return {}
 
     def transport_quota_check(self, response):
         """Implements SWHListerBase.transport_quota_check with standard 429 code
             check for HTTP with Requests library.
 
         MAY BE OVERRIDDEN if the server notifies about rate limits in a
             non-standard way that doesn't use HTTP 429 and the Retry-After
             response header. ( https://tools.ietf.org/html/rfc6585#section-4 )
         """
         if response.status_code == 429:  # HTTP too many requests
             retry_after = response.headers.get('Retry-After', self.back_off())
             try:
                 # might be seconds
                 return True, float(retry_after)
             except:
                 # might be http-date
                 at_date = datetime(*parsedate(retry_after)[:6])
                 from_now = (at_date - datetime.today()).total_seconds() + 5
                 return True, max(0, from_now)
         else:  # response ok
             self.reset_backoff()
             return False, 0
 
     def __init__(self, api_baseurl=None):
         if not api_baseurl:
             raise NameError('HTTP Lister Transport requires api_baseurl.')
         self.api_baseurl = api_baseurl  # eg. 'https://api.github.com'
         self.session = requests.Session()
 
     def transport_request(self, identifier):
         """Implements SWHListerBase.transport_request for HTTP using Requests.
         """
         path = self.PATH_TEMPLATE % identifier
         params = {}
         params['headers'] = self.request_headers() or {}
         creds = self.config['credentials']
         auth = random.choice(creds) if creds else None
         if auth:
-            params['auth'] = auth
+            params['auth'] = (auth['username'], auth['password'])
         try:
             return self.session.get(self.api_baseurl + path, **params)
         except requests.exceptions.ConnectionError as e:
             raise FetchError(e)
 
     def transport_response_to_string(self, response):
         """Implements SWHListerBase.transport_response_to_string for HTTP given
             Requests responses.
         """
         s = pformat(response.request.path_url)
         s += '\n#\n' + pformat(response.status_code)
         s += '\n#\n' + pformat(response.headers)
         s += '\n#\n'
         try:  # json?
             s += pformat(response.json())
         except:  # not json
             try:  # xml?
                 s += pformat(xmltodict.parse(response.text))
             except:  # not xml
                 s += pformat(response.text)
         return s