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/tests/testdummy/auth.py

@@ -0,0 +1,38 @@
+from collections import OrderedDict
+
+from django import forms
+
+from pretix.base.auth import BaseAuthBackend
+from pretix.base.models import User
+
+
+class TestFormAuthBackend(BaseAuthBackend):
+    identifier = 'test_form'
+    verbose_name = 'Form'
+
+    @property
+    def login_form_fields(self) -> dict:
+        return OrderedDict([
+            ('username', forms.CharField(max_length=100)),
+            ('password', forms.CharField(max_length=100)),
+        ])
+
+    def form_authenticate(self, request, form_data):
+        if form_data['username'] == 'foo' and form_data['password'] == 'bar':
+            return User.objects.get_or_create(
+                email='foo@example.com',
+                auth_backend='test_form'
+            )[0]
+
+
+class TestRequestAuthBackend(BaseAuthBackend):
+    identifier = 'test_request'
+    verbose_name = 'Request'
+    visible = False
+
+    def request_authenticate(self, request):
+        if 'X-Login-Email' in request.headers:
+            return User.objects.get_or_create(
+                email=request.headers['X-Login-Email'],
+                auth_backend='test_request'
+            )[0]