include request in password grant authenticate call

An an example this can be used to help implement measures against brute
force attacks and to alert on or mitigate other untrusted authentication
attempts.

oidc_provider/lib/endpoints/token.py

@@ -1,3 +1,4 @@
+import inspect
 from base64 import urlsafe_b64encode
 import hashlib
 import logging
@@ -96,7 +97,14 @@ class TokenEndpoint(object):
             if not settings.get('OIDC_GRANT_TYPE_PASSWORD_ENABLE'):
                 raise TokenError('unsupported_grant_type')
 
+            auth_args = (self.request,)
+            try:
+                inspect.getcallargs(authenticate, *auth_args)
+            except TypeError:
+                auth_args = ()
+
             user = authenticate(
+                *auth_args,
                 username=self.params['username'],
                 password=self.params['password']
             )

oidc_provider/tests/app/utils.py

@@ -1,5 +1,9 @@
 import random
 import string
+
+import django
+from django.contrib.auth.backends import ModelBackend
+
 try:
     from urlparse import parse_qs, urlsplit
 except ImportError:
@@ -131,3 +135,10 @@ def fake_idtoken_processing_hook2(id_token, user):
 def fake_introspection_processing_hook(response_dict, client, id_token):
     response_dict['test_introspection_processing_hook'] = FAKE_RANDOM_STRING
     return response_dict
+
+
+class TestAuthBackend:
+    def authenticate(self, *args, **kwargs):
+        if django.VERSION[0] >= 2 or (django.VERSION[0] == 1 and django.VERSION[1] >= 11):
+            assert len(args) > 0 and args[0]
+        return ModelBackend().authenticate(*args, **kwargs)

oidc_provider/tests/cases/test_token_endpoint.py

@@ -3,6 +3,7 @@ import time
 import uuid
 
 from base64 import b64encode
+
 try:
     from urllib.parse import urlencode
 except ImportError:
@@ -256,6 +257,17 @@ class TokenTestCase(TestCase):
             else:
                 self.assertNotIn(claim, userinfo)
 
+    @override_settings(OIDC_GRANT_TYPE_PASSWORD_ENABLE=True,
+                       AUTHENTICATION_BACKENDS=("oidc_provider.tests.app.utils.TestAuthBackend",))
+    def test_password_grant_passes_request_to_backend(self):
+        response = self._post_request(
+            post_data=self._password_grant_post_data(),
+            extras=self._password_grant_auth_header()
+        )
+
+        response_dict = json.loads(response.content.decode('utf-8'))
+        self.assertIn('access_token', response_dict)
+
     @override_settings(OIDC_TOKEN_EXPIRE=720)
     def test_authorization_code(self):
         """