keycloak_client: fix diff for keycloak client auth flow overrides (#11455)

* 11430: fix diff for keycloak client auth flow overrides

* 11430: add changelog fragment

* 11430: move util function merge_settings_without_absent_nulls to the util functions file _keycloak_utils

* 11443: code cleanup

---------

Co-authored-by: Thomas Bargetz <thomas.bargetz@rise-world.com>

plugins/module_utils/identity/keycloak/_keycloak_utils.py

@@ -0,0 +1,32 @@
+# Copyright (c) Ansible Project
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# Note that this module util is **PRIVATE** to the collection. It can have breaking changes at any time.
+# Do not use this from other collections or standalone plugins/modules!
+
+from __future__ import annotations
+
+import typing as t
+
+
+def merge_settings_without_absent_nulls(
+    existing_settings: dict[str, t.Any], desired_settings: dict[str, t.Any]
+) -> dict[str, t.Any]:
+    """
+    Merges existing and desired settings into a new dictionary while excluding null values in desired settings that are absent in the existing settings.
+    This ensures idempotency by treating absent keys in existing settings and null values in desired settings as equivalent, preventing unnecessary updates.
+
+    Args:
+      existing_settings (dict): Dictionary representing the current settings in Keycloak
+      desired_settings (dict): Dictionary representing the desired settings
+
+    Returns:
+      dict: A new dictionary containing all entries from existing_settings and desired_settings,
+      excluding null values in desired_settings whose corresponding keys are not present in existing_settings
+    """
+
+    existing = existing_settings or {}
+    desired = desired_settings or {}
+
+    return {**existing, **{k: v for k, v in desired.items() if v is not None or k in existing}}