Add refresh_events to CertHandler (#108)

* refresh events

* static check

* lint

* nit + speed up tests

* improve doc

* revert init

* refactor

* use hashing

lib/charms/observability_libs/v1/cert_handler.py

@@ -59,15 +59,15 @@
 import logging
 
 from ops.charm import CharmBase
-from ops.framework import EventBase, EventSource, Object, ObjectEvents
+from ops.framework import BoundEvent, EventBase, EventSource, Object, ObjectEvents, StoredState
 from ops.jujuversion import JujuVersion
 from ops.model import Relation, Secret, SecretNotFoundError
 
 logger = logging.getLogger(__name__)
 
 LIBID = "b5cd5cd580f3428fa5f59a8876dcbe6a"
 LIBAPI = 1
-LIBPATCH = 11
+LIBPATCH = 12
 
 VAULT_SECRET_LABEL = "cert-handler-private-vault"
 
@@ -273,6 +273,7 @@ class CertHandler(Object):
     """A wrapper for the requirer side of the TLS Certificates charm library."""
 
     on = CertHandlerEvents()  # pyright: ignore
+    _stored = StoredState()
 
     def __init__(
         self,
@@ -283,6 +284,7 @@ def __init__(
         peer_relation_name: str = "peers",
         cert_subject: Optional[str] = None,
         sans: Optional[List[str]] = None,
+        refresh_events: Optional[List[BoundEvent]] = None,
     ):
         """CertHandler is used to wrap TLS Certificates management operations for charms.
 
@@ -299,8 +301,17 @@ def __init__(
                 Must match metadata.yaml.
             cert_subject: Custom subject. Name collisions are under the caller's responsibility.
             sans: DNS names. If none are given, use FQDN.
+            refresh_events: an optional list of bound events which
+                will be observed to replace the current CSR with a new one
+                if there are changes in the CSR's DNS SANs or IP SANs.
+                Then, subsequently, replace its corresponding certificate with a new one.
         """
         super().__init__(charm, key)
+        # use StoredState to store the hash of the CSR
+        # to potentially trigger a CSR renewal on `refresh_events`
+        self._stored.set_default(
+            csr_hash=None,
+        )
         self.charm = charm
 
         # We need to sanitize the unit name, otherwise route53 complains:
@@ -355,6 +366,15 @@ def __init__(
             self._on_upgrade_charm,
         )
 
+        if refresh_events:
+            for ev in refresh_events:
+                self.framework.observe(ev, self._on_refresh_event)
+
+    def _on_refresh_event(self, _):
+        """Replace the latest current CSR with a new one if there are any SANs changes."""
+        if self._stored.csr_hash != self._csr_hash:
+            self._generate_csr(renew=True)
+
     def _on_upgrade_charm(self, _):
         has_privkey = self.vault.get_value("private-key")
 
@@ -419,6 +439,20 @@ def enabled(self) -> bool:
 
         return True
 
+    @property
+    def _csr_hash(self) -> int:
+        """A hash of the config that constructs the CSR.
+
+        Only include here the config options that, should they change, should trigger a renewal of
+        the CSR.
+        """
+        return hash(
+            (
+                tuple(self.sans_dns),
+                tuple(self.sans_ip),
+            )
+        )
+
     @property
     def available(self) -> bool:
         """Return True if all certs are available in relation data; False otherwise."""
@@ -484,6 +518,8 @@ def _generate_csr(
                 )
                 self.certificates.request_certificate_creation(certificate_signing_request=csr)
 
+            self._stored.csr_hash = self._csr_hash
+
         if clear_cert:
             self.vault.clear()
 

tests/scenario/test_cert_handler/test_cert_handler_v1.py

@@ -1,8 +1,13 @@
 import socket
 import sys
+from contextlib import contextmanager
 from pathlib import Path
+from unittest.mock import patch
 
 import pytest
+from cryptography import x509
+from cryptography.hazmat.backends import default_backend
+from cryptography.x509.oid import ExtensionOID
 from ops import CharmBase
 from scenario import Context, PeerRelation, Relation, State
 
@@ -12,6 +17,7 @@
 
 libs = str(Path(__file__).parent.parent.parent.parent / "lib")
 sys.path.append(libs)
+MOCK_HOSTNAME = "mock-hostname"
 
 
 class MyCharm(CharmBase):
@@ -22,8 +28,28 @@ class MyCharm(CharmBase):
 
     def __init__(self, fw):
         super().__init__(fw)
+        sans = [socket.getfqdn()]
+        if hostname := self._mock_san:
+            sans.append(hostname)
 
-        self.ch = CertHandler(self, key="ch", sans=[socket.getfqdn()])
+        self.ch = CertHandler(self, key="ch", sans=sans, refresh_events=[self.on.config_changed])
+
+    @property
+    def _mock_san(self):
+        """This property is meant to be mocked to return a mock string hostname to be used as SAN.
+
+        By default, it returns None.
+        """
+        return None
+
+
+def get_csr_obj(csr: str):
+    return x509.load_pem_x509_csr(csr.encode(), default_backend())
+
+
+def get_sans_from_csr(csr):
+    san_extension = csr.extensions.get_extension_for_oid(ExtensionOID.SUBJECT_ALTERNATIVE_NAME)
+    return set(san_extension.value.get_values_for_type(x509.DNSName))
 
 
 @pytest.fixture
@@ -36,6 +62,20 @@ def certificates():
     return Relation("certificates")
 
 
+@contextmanager
+def _sans_patch(hostname=MOCK_HOSTNAME):
+    with patch.object(MyCharm, "_mock_san", hostname):
+        yield
+
+
+@contextmanager
+def _cert_renew_patch():
+    with patch(
+        "charms.tls_certificates_interface.v3.tls_certificates.TLSCertificatesRequiresV3.request_certificate_renewal"
+    ) as patcher:
+        yield patcher
+
+
 @pytest.mark.parametrize("leader", (True, False))
 def test_cert_joins(ctx, certificates, leader):
     with ctx.manager(
@@ -72,3 +112,65 @@ def test_cert_joins_peer_vault_backend(ctx_juju2, certificates, leader):
     ) as mgr:
         mgr.run()
         assert mgr.charm.ch.private_key
+
+
+def test_renew_csr_on_sans_change(ctx, certificates):
+    # generate a CSR
+    with ctx.manager(
+        certificates.joined_event,
+        State(leader=True, relations=[certificates]),
+    ) as mgr:
+        charm = mgr.charm
+        state_out = mgr.run()
+        orig_csr = get_csr_obj(charm.ch._csr)
+        assert get_sans_from_csr(orig_csr) == {socket.getfqdn()}
+
+    # trigger a config_changed with a modified SAN
+    with _sans_patch():
+        with ctx.manager("config_changed", state_out) as mgr:
+            charm = mgr.charm
+            state_out = mgr.run()
+            csr = get_csr_obj(charm.ch._csr)
+            # assert CSR contains updated SAN
+            assert get_sans_from_csr(csr) == {socket.getfqdn(), MOCK_HOSTNAME}
+
+
+def test_csr_no_change_on_wrong_refresh_event(ctx, certificates):
+    with _cert_renew_patch() as renew_patch:
+        with ctx.manager(
+            "config_changed",
+            State(leader=True, relations=[certificates]),
+        ) as mgr:
+            charm = mgr.charm
+            state_out = mgr.run()
+            orig_csr = get_csr_obj(charm.ch._csr)
+            assert get_sans_from_csr(orig_csr) == {socket.getfqdn()}
+
+    with _sans_patch():
+        with _cert_renew_patch() as renew_patch:
+            with ctx.manager("update_status", state_out) as mgr:
+                charm = mgr.charm
+                state_out = mgr.run()
+                csr = get_csr_obj(charm.ch._csr)
+                assert get_sans_from_csr(csr) == {socket.getfqdn()}
+                assert renew_patch.call_count == 0
+
+
+def test_csr_no_change(ctx, certificates):
+
+    with ctx.manager(
+        "config_changed",
+        State(leader=True, relations=[certificates]),
+    ) as mgr:
+        charm = mgr.charm
+        state_out = mgr.run()
+        orig_csr = get_csr_obj(charm.ch._csr)
+        assert get_sans_from_csr(orig_csr) == {socket.getfqdn()}
+
+    with _cert_renew_patch() as renew_patch:
+        with ctx.manager("config_changed", state_out) as mgr:
+            charm = mgr.charm
+            state_out = mgr.run()
+            csr = get_csr_obj(charm.ch._csr)
+            assert get_sans_from_csr(csr) == {socket.getfqdn()}
+            assert renew_patch.call_count == 0

tests/unit/test_kubernetes_compute_resources.py

@@ -2,9 +2,10 @@
 # See LICENSE file for licensing details.
 import unittest
 from unittest import mock
-from unittest.mock import MagicMock, Mock
+from unittest.mock import MagicMock, Mock, patch
 
 import httpx
+import tenacity
 import yaml
 from charms.observability_libs.v0.kubernetes_compute_resources_patch import (
     KubernetesComputeResourcesPatch,
@@ -16,12 +17,22 @@
 from ops import BlockedStatus, WaitingStatus
 from ops.charm import CharmBase
 from ops.testing import Harness
+from pytest import fixture
 
 from tests.unit.helpers import PROJECT_DIR
 
 CL_PATH = "charms.observability_libs.v0.kubernetes_compute_resources_patch.KubernetesComputeResourcesPatch"
 
 
+@fixture(autouse=True)
+def patch_retry():
+    with patch.multiple(
+        KubernetesComputeResourcesPatch,
+        PATCH_RETRY_STOP=tenacity.stop_after_delay(0),
+    ):
+        yield
+
+
 class TestKubernetesComputeResourcesPatch(unittest.TestCase):
     class _TestCharm(CharmBase):
         def __init__(self, *args):

tox.ini

@@ -111,5 +111,6 @@ allowlist_externals =
     rm
 commands =
     charmcraft fetch-lib charms.tls_certificates_interface.v2.tls_certificates
+    charmcraft fetch-lib charms.tls_certificates_interface.v3.tls_certificates
     pytest -v --tb native {[vars]tst_path}/scenario --log-cli-level=INFO -s {posargs}
     rm -rf ./lib/charms/tls_certificates_interface