Add class for keystone audit middleware testing

Added general class for testing keystone audit middleware
functionality in charms. Tests correct rendering of
api-paste.ini file.

Example usage with charm Heat:

tests/tests.yaml

tests:
  - zaza.openstack.charm_tests.audit.tests.KeystoneAuditMiddlewareTest

tests_options:
  audit-middleware:
    service: heat

zaza/openstack/charm_tests/audit/__init__.py

@@ -0,0 +1,20 @@
+# Copyright 2024 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Keystone audit middleware.
+
+Collection of code for setting up and testing Keystone audit middleware
+functionality.
+"""

zaza/openstack/charm_tests/audit/tests.py

@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+#
+# Copyright 2024 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Keystone audit middleware API logging testing.
+
+These methods test the
+rendering of the charm's api-paste.ini file to ensure the appropriate sections
+are rendered or not rendered depending on the state of the audit-middleware
+configuration option.
+"""
+
+import logging
+import zaza.model
+import zaza.openstack.charm_tests.test_utils as test_utils
+
+
+class KeystoneAuditMiddlewareBaseTest(test_utils.OpenStackBaseTest):
+    """Base class for Keystone audit middleware tests."""
+
+    @classmethod
+    def setUpClass(cls):
+        """Run class setup for Keystone audit middleware tests."""
+        super(KeystoneAuditMiddlewareBaseTest, cls).setUpClass()
+        test_config = cls.test_config['tests_options']['audit-middleware']
+        cls.service_name = test_config['service']
+        cls.lead_unit = zaza.model.get_lead_unit_name(
+            cls.service_name,
+            model_name=cls.model_name
+        )
+        logging.info('Leader unit is %s', cls.lead_unit)
+        logging.info('Service name is %s', cls.service_name)
+
+    def fetch_api_paste_content(self):
+        """Fetch content of api-paste.ini file."""
+        api_paste_ini_path = f"/etc/{self.service_name}/api-paste.ini"
+        try:
+            return zaza.model.file_contents(
+                self.lead_unit,
+                api_paste_ini_path,
+            )
+        except zaza.model.CommandRunFailed as e:
+            self.fail("Error fetching api-paste.ini: {}".format(str(e)))
+
+
+class KeystoneAuditMiddlewareTest(KeystoneAuditMiddlewareBaseTest):
+    """Keystone audit middleware API logging feature tests."""
+
+    def test_101_apipaste_includes_audit_section(self):
+        """Test api-paste.ini renders audit section when enabled."""
+        expected_content = [
+            "[filter:audit]",
+            "paste.filter_factory = keystonemiddleware.audit:filter_factory",
+            f"audit_map_file = /etc/{self.service_name}/api_audit_map.conf",
+            f"service_name = {self.service_name}"
+        ]
+
+        set_default = {'audit-middleware': False}
+        set_alternate = {'audit-middleware': True}
+
+        with self.config_change(default_config=set_default,
+                                alternate_config=set_alternate,
+                                application_name=self.service_name):
+            api_paste_content = self.fetch_api_paste_content()
+            for line in expected_content:
+                self.assertIn(line, api_paste_content)
+
+    def test_102_apipaste_excludes_audit_section(self):
+        """Test api_paste.ini does not render audit section when disabled."""
+        section_heading = '[filter:audit]'
+
+        if not self.config_current(self.service_name)['audit-middleware']:
+            api_paste_content = self.fetch_api_paste_content()
+            self.assertNotIn(section_heading, api_paste_content)
+        else:
+            self.fail("Failed due to audit-middleware being incorrectly set to\
+                      True")