api: add page size parameter to user's API (#54514)

The query param is named `limit`.

src/authentic2/api_views.py

@@ -717,6 +717,11 @@ class FreeTextSearchFilter(BaseFilterBackend):
         return queryset
 
 
+class UsersAPIPagination(pagination.CursorPagination):
+    page_size_query_param = 'limit'
+    max_page_size = 100
+
+
 class UsersAPI(api_mixins.GetOrCreateMixinView, HookMixin, ExceptionHandlerMixin, ModelViewSet):
     queryset = User.objects.all()
     ordering_fields = ['username', 'first_name', 'last_name', 'modified', 'date_joined']
@@ -730,7 +735,7 @@ class UsersAPI(api_mixins.GetOrCreateMixinView, HookMixin, ExceptionHandlerMixin
     filter_class = UsersFilter
     filterset_class = UsersFilter
     filter_backends = [FreeTextSearchFilter] + api_settings.DEFAULT_FILTER_BACKENDS
-    pagination_class = pagination.CursorPagination
+    pagination_class = UsersAPIPagination
 
     @property
     def ordering(self):

tests/test_api.py

@@ -2544,3 +2544,15 @@ def test_find_duplicates_put(app, admin, settings):
     app.put_json(
         '/api/users/find_duplicates/', params={'first_name': 'Eleonore', 'last_name': 'aeiou'}, status=405
     )
+
+
+def test_users_page_size(app, admin):
+    app.authorization = ('Basic', (admin.username, admin.username))
+
+    User.objects.create()
+
+    resp = app.get('/api/users/')
+    assert len(resp.json['results']) == 2
+
+    resp = app.get('/api/users/?limit=1')
+    assert len(resp.json['results']) == 1