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