stages/user_write: dynamic groups (#2901)

* stages/user_write: add dynamic groups

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

* simplify functions

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

website/docs/flow/stages/user_write.md

@@ -5,3 +5,15 @@ title: User write stage
 This stages writes data from the current context to the current pending user. If no user is pending, a new one is created.
 
 Newly created users can be created as inactive and can be assigned to a selected group.
+
+### Dynamic groups
+
+Starting with authentik 2022.5, users can be added to dynamic groups. To do so, simply set `groups` in the flow plan context before this stage is run, for example
+
+```python
+from authentik.core.models import Group
+group, _ = Group.objects.get_or_create(name="some-group")
+# ["groups"] *must* be set to an array of Group objects, names alone are not enough.
+request.context["groups"] = [group]
+return True
+```