Make next url authentication backend dependent (#1609)

* Make next url authentication backend dependent

* Rename authentication next_url to get_next_url.

* Add test for custom authentication backend get_next_url.

* Fix typo in docstring of authentication backend get_next_url.

src/pretix/base/auth.py

@@ -85,6 +85,16 @@ class BaseAuthBackend:
         """
         return
 
+    def get_next_url(self, request):
+        """
+        This method will be called after a successful login to determine the next URL. Pretix in general uses the
+        ``'next'`` query parameter. However, external authentication methods could use custom attributes with hardcoded
+        names for security purposes. For example, OAuth uses ``'state'`` for keeping track of application state.
+        """
+        if "next" in request.GET:
+            return request.GET.get("next")
+        return None
+
 
 class NativeAuthBackend(BaseAuthBackend):
     identifier = 'native'

src/pretix/control/views/auth.py

@@ -39,18 +39,19 @@ def process_login(request, user, keep_logged_in):
     :return: This method returns a ``HttpResponse``.
     """
     request.session['pretix_auth_long_session'] = settings.PRETIX_LONG_SESSIONS and keep_logged_in
+    next_url = get_auth_backends()[user.auth_backend].get_next_url(request)
     if user.require_2fa:
         request.session['pretix_auth_2fa_user'] = user.pk
         request.session['pretix_auth_2fa_time'] = str(int(time.time()))
         twofa_url = reverse('control:auth.login.2fa')
-        if "next" in request.GET and is_safe_url(request.GET.get("next"), allowed_hosts=None):
-            twofa_url += '?next=' + quote(request.GET.get('next'))
+        if next_url and is_safe_url(next_url, allowed_hosts=None):
+            twofa_url += '?next=' + quote(next_url)
         return redirect(twofa_url)
     else:
         auth_login(request, user)
         request.session['pretix_auth_login_time'] = int(time.time())
-        if "next" in request.GET and is_safe_url(request.GET.get("next"), allowed_hosts=None):
-            return redirect(request.GET.get("next"))
+        if next_url and is_safe_url(next_url, allowed_hosts=None):
+            return redirect(next_url)
         return redirect(reverse('control:index'))
 
 
@@ -72,7 +73,8 @@ def login(request):
     if not backend.visible:
         backend = [b for b in backends if b.visible][0]
     if request.user.is_authenticated:
-        return redirect(request.GET.get("next", 'control:index'))
+        next_url = backend.get_next_url(request) or 'control:index'
+        return redirect(next_url)
     if request.method == 'POST':
         form = LoginForm(backend=backend, data=request.POST)
         if form.is_valid() and form.user_cache and form.user_cache.auth_backend == backend.identifier:

src/pretix/control/views/user.py

@@ -101,18 +101,21 @@ class ReauthView(TemplateView):
             t = int(time.time())
             request.session['pretix_auth_login_time'] = t
             request.session['pretix_auth_last_used'] = t
-            if "next" in request.GET and is_safe_url(request.GET.get("next"), allowed_hosts=None):
-                return redirect(request.GET.get("next"))
+            next_url = get_auth_backends()[request.user.auth_backend].get_next_url(request)
+            if next_url and is_safe_url(next_url, allowed_hosts=None):
+                return redirect(next_url)
             return redirect(reverse('control:index'))
         else:
             messages.error(request, _('The password you entered was invalid, please try again.'))
             return self.get(request, *args, **kwargs)
 
     def get(self, request, *args, **kwargs):
-        u = get_auth_backends()[request.user.auth_backend].request_authenticate(request)
+        backend = get_auth_backends()[request.user.auth_backend]
+        u = backend.request_authenticate(request)
         if u and u == request.user:
-            if "next" in request.GET and is_safe_url(request.GET.get("next"), allowed_hosts=None):
-                return redirect(request.GET.get("next"))
+            next_url = backend.get_next_url(request)
+            if next_url and is_safe_url(next_url, allowed_hosts=None):
+                return redirect(next_url)
             return redirect(reverse('control:index'))
         return super().get(request, *args, **kwargs)
 

src/tests/control/test_auth.py

@@ -148,6 +148,11 @@ class LoginFormTest(TestCase):
         response = self.client.get('/control/')
         assert b'hallo@example.org' in response.content
 
+    def test_custom_get_next_url(self):
+        response = self.client.get('/control/login?state=/control/events/', HTTP_X_LOGIN_EMAIL='hallo@example.org')
+        self.assertEqual(response.status_code, 302)
+        self.assertIn('/control/events/', response['Location'])
+
 
 class RegistrationFormTest(TestCase):
 

src/tests/testdummy/auth.py

@@ -36,3 +36,8 @@ class TestRequestAuthBackend(BaseAuthBackend):
                 email=request.headers['X-Login-Email'],
                 auth_backend='test_request'
             )[0]
+
+    def get_next_url(self, request):
+        if 'state' in request.GET:
+            return request.GET.get('state')
+        return None