Refs #775 -- Pluggable authentication backends (#1447)

* Drag-and-drop: Force csrf_token to be present

* Rough design

* Missing file

* b.visble

* Forms

* Docs

* Tests

* Fix variable

src/pretix/base/auth.py

@@ -0,0 +1,109 @@
+from collections import OrderedDict
+from importlib import import_module
+
+from django import forms
+from django.conf import settings
+from django.contrib.auth import authenticate
+from django.utils.translation import gettext_lazy as _
+
+
+def get_auth_backends():
+    backends = {}
+    for b in settings.PRETIX_AUTH_BACKENDS:
+        mod, name = b.rsplit('.', 1)
+        b = getattr(import_module(mod), name)()
+        backends[b.identifier] = b
+    return backends
+
+
+class BaseAuthBackend:
+    """
+    This base class defines the interface that needs to be implemented by every class that supplies
+    an authentication method to pretix. Please note that pretix authentication backends are different
+    from plain Django authentication backends! Be sure to read the documentation chapter on authentication
+    backends before you implement one.
+    """
+
+    @property
+    def identifier(self):
+        """
+        A short and unique identifier for this authentication backend.
+        This should only contain lowercase letters and in most cases will
+        be the same as your package name.
+        """
+        raise NotImplementedError()
+
+    @property
+    def verbose_name(self):
+        """
+        A human-readable name of this authentication backend.
+        """
+        raise NotImplementedError()
+
+    @property
+    def visible(self):
+        """
+        Whether or not this backend can be selected by users actively. Set this to ``False``
+        if you only implement ``request_authenticate``.
+        """
+        return True
+
+    @property
+    def login_form_fields(self) -> dict:
+        """
+        This property may return form fields that the user needs to fill in to log in.
+        """
+        return {}
+
+    def form_authenticate(self, request, form_data):
+        """
+        This method will be called after the user filled in the login form. ``request`` will contain
+        the current request and ``form_data`` the input for the form fields defined in ``login_form_fields``.
+        You are expected to either return a ``User`` object (if login was successful) or ``None``.
+        """
+        return
+
+    def request_authenticate(self, request):
+        """
+        This method will be called when the user opens the login form. If the user already has a valid session
+        according to your login mechanism, for example a cookie set by a different system or HTTP header set by a
+        reverse proxy, you can directly return a ``User`` object that will be logged in.
+
+        ``request`` will contain the current request.
+        You are expected to either return a ``User`` object (if login was successful) or ``None``.
+        """
+        return
+
+    def authentication_url(self, request):
+        """
+        This method will be called to populate the URL for your authentication method's tab on the login page.
+        For example, if your method works through OAuth, you could return the URL of the OAuth authorization URL the
+        user needs to visit.
+
+        If you return ``None`` (the default), the link will point to a page that shows the form defined by
+        ``login_form_fields``.
+        """
+        return
+
+
+class NativeAuthBackend(BaseAuthBackend):
+    identifier = 'native'
+    verbose_name = _('pretix User')
+
+    @property
+    def login_form_fields(self) -> dict:
+        """
+        This property may return form fields that the user needs to fill in
+        to log in.
+        """
+        d = OrderedDict([
+            ('email', forms.EmailField(label=_("E-mail"), max_length=254,
+                                       widget=forms.EmailInput(attrs={'autofocus': 'autofocus'}))),
+            ('password', forms.CharField(label=_("Password"), widget=forms.PasswordInput)),
+        ])
+        return d
+
+    def form_authenticate(self, request, form_data):
+        u = authenticate(request=request, email=form_data['email'].lower(), password=form_data['password'])
+        if u and u.auth_backend == self.identifier:
+            return u

src/pretix/base/forms/auth.py

@@ -1,6 +1,5 @@
 from django import forms
 from django.conf import settings
-from django.contrib.auth import authenticate
 from django.contrib.auth.password_validation import (
     password_validators_help_texts, validate_password,
 )
@@ -14,32 +13,33 @@ class LoginForm(forms.Form):
     Base class for authenticating users. Extend this to get a form that accepts
     username/password logins.
     """
-    email = forms.EmailField(label=_("E-mail"), max_length=254, widget=forms.EmailInput(attrs={'autofocus': 'autofocus'}))
-    password = forms.CharField(label=_("Password"), widget=forms.PasswordInput)
     keep_logged_in = forms.BooleanField(label=_("Keep me logged in"), required=False)
 
     error_messages = {
-        'invalid_login': _("Please enter a correct email address and password."),
+        'invalid_login': _("This combination of credentials is not known to our system."),
         'inactive': _("This account is inactive.")
     }
 
-    def __init__(self, request=None, *args, **kwargs):
+    def __init__(self, backend, request=None, *args, **kwargs):
         """
         The 'request' parameter is set for custom auth use by subclasses.
         The form data comes in via the standard 'data' kwarg.
         """
         self.request = request
         self.user_cache = None
+        self.backend = backend
         super().__init__(*args, **kwargs)
+        for k, f in backend.login_form_fields.items():
+            self.fields[k] = f
+
         if not settings.PRETIX_LONG_SESSIONS:
             del self.fields['keep_logged_in']
+        else:
+            self.fields.move_to_end('keep_logged_in')
 
     def clean(self):
-        email = self.cleaned_data.get('email')
-        password = self.cleaned_data.get('password')
-
-        if email and password:
-            self.user_cache = authenticate(request=self.request, email=email.lower(), password=password)
+        if all(k in self.cleaned_data for k, f in self.fields.items() if f.required):
+            self.user_cache = self.backend.form_authenticate(self.request, self.cleaned_data)
             if self.user_cache is None:
                 raise forms.ValidationError(
                     self.error_messages['invalid_login'],
@@ -181,3 +181,44 @@ class PasswordForgotForm(forms.Form):
 
     def clean_email(self):
         return self.cleaned_data['email']
+
+
+class ReauthForm(forms.Form):
+    error_messages = {
+        'invalid_login': _("This combination of credentials is not known to our system."),
+        'inactive': _("This account is inactive.")
+    }
+
+    def __init__(self, backend, user, request=None, *args, **kwargs):
+        """
+        The 'request' parameter is set for custom auth use by subclasses.
+        The form data comes in via the standard 'data' kwarg.
+        """
+        self.request = request
+        self.user = user
+        self.backend = backend
+        super().__init__(*args, **kwargs)
+        for k, f in backend.login_form_fields.items():
+            self.fields[k] = f
+        if 'email' in self.fields:
+            self.fields['email'].disabled = True
+
+    def clean(self):
+        self.cleaned_data['email'] = self.user.email
+        user_cache = self.backend.form_authenticate(self.request, self.cleaned_data)
+        if user_cache != self.user:
+            raise forms.ValidationError(
+                self.error_messages['invalid_login'],
+                code='invalid_login'
+            )
+        else:
+            self.confirm_login_allowed(user_cache)
+
+        return self.cleaned_data
+
+    def confirm_login_allowed(self, user: User):
+        if not user.is_active:
+            raise forms.ValidationError(
+                self.error_messages['inactive'],
+                code='inactive',
+            )

src/pretix/base/forms/user.py

@@ -56,6 +56,11 @@ class UserSettingsForm(forms.ModelForm):
         self.user = kwargs.pop('user')
         super().__init__(*args, **kwargs)
         self.fields['email'].required = True
+        if self.user.auth_backend != 'native':
+            del self.fields['old_pw']
+            del self.fields['new_pw']
+            del self.fields['new_pw_repeat']
+            self.fields['email'].disabled = True
 
     def clean_old_pw(self):
         old_pw = self.cleaned_data.get('old_pw')

src/pretix/base/migrations/0137_auto_20191015_1141.py

@@ -0,0 +1,17 @@
+# Generated by Django 2.2.4 on 2019-10-15 11:41
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('pretixbase', '0136_auto_20190918_1742'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='user',
+            name='auth_backend',
+            field=models.CharField(default='native', max_length=255),
+        ),
+    ]

src/pretix/base/models/auth.py

@@ -109,6 +109,7 @@ class User(AbstractBaseUser, PermissionsMixin, LoggingMixin):
         help_text=_('If turned off, you will not get any notifications.')
     )
     notifications_token = models.CharField(max_length=255, default=generate_notifications_token)
+    auth_backend = models.CharField(max_length=255, default='native')
 
     objects = UserManager()