rewrite PasswordFactor to use backends setting instead of trying all backends

passbook/core/auth/factors/password.py

@@ -1,8 +1,10 @@
 """passbook multi-factor authentication engine"""
+from inspect import Signature
 from logging import getLogger
 
 from django.contrib import messages
-from django.contrib.auth import authenticate
+from django.contrib.auth import _clean_credentials
+from django.contrib.auth.signals import user_login_failed
 from django.core.exceptions import PermissionDenied
 from django.forms.utils import ErrorList
 from django.shortcuts import redirect, reverse
@@ -15,10 +17,40 @@ from passbook.core.forms.authentication import PasswordFactorForm
 from passbook.core.models import Nonce
 from passbook.core.tasks import send_email
 from passbook.lib.config import CONFIG
+from passbook.lib.utils.reflection import path_to_class
 
 LOGGER = getLogger(__name__)
 
 
+def authenticate(request, backends, **credentials):
+    """If the given credentials are valid, return a User object.
+    Customized version of django's authenticate, which accepts a list of backends"""
+    for backend_path in backends:
+        backend = path_to_class(backend_path)()
+        try:
+            signature = Signature.from_callable(backend.authenticate)
+            signature.bind(request, **credentials)
+        except TypeError:
+            LOGGER.debug("Backend %s doesn't accept our arguments", backend)
+            # This backend doesn't accept these credentials as arguments. Try the next one.
+            continue
+        LOGGER.debug('Attempting authentication with %s...', backend)
+        try:
+            user = backend.authenticate(request, **credentials)
+        except PermissionDenied:
+            LOGGER.debug('Backend %r threw PermissionDenied', backend)
+            # This backend says to stop in our tracks - this user should not be allowed in at all.
+            break
+        if user is None:
+            continue
+        # Annotate the user object with the path of the backend.
+        user.backend = backend_path
+        return user
+
+    # The credentials supplied are invalid to all backends, fire signal
+    user_login_failed.send(sender=__name__, credentials=_clean_credentials(
+        credentials), request=request)
+
 class PasswordFactor(FormView, AuthenticationFactor):
     """Authentication factor which authenticates against django's AuthBackend"""
 
@@ -57,7 +89,7 @@ class PasswordFactor(FormView, AuthenticationFactor):
         for uid_field in uid_fields:
             kwargs[uid_field] = getattr(self.authenticator.pending_user, uid_field)
         try:
-            user = authenticate(self.request, **kwargs)
+            user = authenticate(self.request, self.authenticator.current_factor.backends, **kwargs)
             if user:
                 # User instance returned from authenticate() has .backend property set
                 self.authenticator.pending_user = user