diff --git a/mellon/backends.py b/mellon/backends.py
index 0e4726b..add3c49 100644
--- a/mellon/backends.py
+++ b/mellon/backends.py
@@ -14,19 +14,26 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 from __future__ import unicode_literals
+import logging
 
 from django.contrib.auth.backends import ModelBackend
 
 from . import utils
 
+logger = logging.getLogger(__name__)
+
 
 class SAMLBackend(ModelBackend):
     def authenticate(self, request=None, **credentials):
         saml_attributes = credentials.get('saml_attributes') or {}
         # without an issuer we can do nothing
         if 'issuer' not in saml_attributes:
-            return
+            logger.debug('no idp in saml_attributes')
+            return None
         idp = utils.get_idp(saml_attributes['issuer'])
+        if not idp:
+            logger.debug('unknown idp %s', saml_attributes['issuer'])
+            return None
         adapters = utils.get_adapters(idp)
         for adapter in adapters:
             if not hasattr(adapter, 'authorize'):
diff --git a/mellon/views.py b/mellon/views.py
index 1d8d08b..637fcd7 100644
--- a/mellon/views.py
+++ b/mellon/views.py
@@ -130,7 +130,7 @@ class LoginView(ProfileMixin, LogMixin, View):
             for idp in utils.get_idps():
                 return idp
             else:
-                return None
+                return {}
         else:
             return utils.get_idp(entity_id)
 
@@ -305,7 +305,6 @@ class LoginView(ProfileMixin, LogMixin, View):
                 'no entity id found for this artifact %r' % artifact)
         idp = utils.get_idp(login.remoteProviderId)
         if not idp:
-            self.log.warning('entity id %r is unknown', login.remoteProviderId)
             return HttpResponseBadRequest(
                 'entity id %r is unknown' % login.remoteProviderId)
         verify_ssl_certificate = utils.get_setting(