chore: Update charm libraries

lib/charms/tls_certificates_interface/v4/tls_certificates.py

@@ -9,7 +9,7 @@
 Pre-requisites:
   - Juju >= 3.0
   - cryptography >= 43.0.0
-  - pydantic
+  - pydantic >= 2.0
 
 Learn more on how-to use the TLS Certificates interface library by reading the documentation:
 - https://charmhub.io/tls-certificates-interface/
@@ -52,9 +52,12 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 7
+LIBPATCH = 8
 
-PYDEPS = ["cryptography", "pydantic"]
+PYDEPS = [
+    "cryptography>=43.0.0",
+    "pydantic>=2.0",
+]
 
 logger = logging.getLogger(__name__)
 
@@ -211,6 +214,27 @@ def from_string(cls, private_key: str) -> "PrivateKey":
         """Create a PrivateKey object from a private key."""
         return cls(raw=private_key.strip())
 
+    def is_valid(self) -> bool:
+        """Validate that the private key is PEM-formatted, RSA, and at least 2048 bits."""
+        try:
+            key = serialization.load_pem_private_key(
+                self.raw.encode(),
+                password=None,
+            )
+
+            if not isinstance(key, rsa.RSAPrivateKey):
+                logger.warning("Private key is not an RSA key")
+                return False
+
+            if key.key_size < 2048:
+                logger.warning("RSA key size is less than 2048 bits")
+                return False
+
+            return True
+        except ValueError:
+            logger.warning("Invalid private key format")
+            return False
+
 
 @dataclass(frozen=True)
 class Certificate:
@@ -612,12 +636,14 @@ def generate_private_key(
     """Generate a private key with the RSA algorithm.
 
     Args:
-        key_size (int): Key size in bytes
+        key_size (int): Key size in bits, must be at least 2048 bits
         public_exponent: Public exponent.
 
     Returns:
         PrivateKey: Private Key
     """
+    if key_size < 2048:
+        raise ValueError("Key size must be at least 2048 bits for RSA security")
     private_key = rsa.generate_private_key(
         public_exponent=public_exponent,
         key_size=key_size,
@@ -978,6 +1004,7 @@ def __init__(
         certificate_requests: List[CertificateRequestAttributes],
         mode: Mode = Mode.UNIT,
         refresh_events: List[BoundEvent] = [],
+        private_key: Optional[PrivateKey] = None,
     ):
         """Create a new instance of the TLSCertificatesRequiresV4 class.
 
@@ -989,6 +1016,12 @@ def __init__(
             mode (Mode): Whether to use unit or app certificates mode. Default is Mode.UNIT.
             refresh_events (List[BoundEvent]): A list of events to trigger a refresh of
               the certificates.
+            private_key (Optional[PrivateKey]): The private key to use for the certificates.
+                If provided, it will be used instead of generating a new one.
+                If the key is not valid an exception will be raised.
+                Using this parameter is discouraged,
+                having to pass around private keys manually can be a security concern.
+                Allowing the library to generate and manage the key is the more secure approach.
         """
         super().__init__(charm, relationship_name)
         if not JujuVersion.from_environ().has_secrets:
@@ -1002,6 +1035,9 @@ def __init__(
         self.relationship_name = relationship_name
         self.certificate_requests = certificate_requests
         self.mode = mode
+        if private_key and not private_key.is_valid():
+            raise TLSCertificatesError("Invalid private key")
+        self._private_key = private_key
         self.framework.observe(charm.on[relationship_name].relation_created, self._configure)
         self.framework.observe(charm.on[relationship_name].relation_changed, self._configure)
         self.framework.observe(charm.on.secret_expired, self._on_secret_expired)
@@ -1020,10 +1056,10 @@ def _configure(self, _: EventBase):
         if not self._tls_relation_created():
             logger.debug("TLS relation not created yet.")
             return
-        self._generate_private_key()
+        self._ensure_private_key()
+        self._cleanup_certificate_requests()
         self._send_certificate_requests()
         self._find_available_certificates()
-        self._cleanup_certificate_requests()
 
     def _mode_is_valid(self, mode: Mode) -> bool:
         return mode in [Mode.UNIT, Mode.APP]
@@ -1114,45 +1150,91 @@ def _get_app_or_unit(self) -> Union[Application, Unit]:
     @property
     def private_key(self) -> Optional[PrivateKey]:
         """Return the private key."""
+        if self._private_key:
+            return self._private_key
         if not self._private_key_generated():
             return None
         secret = self.charm.model.get_secret(label=self._get_private_key_secret_label())
         private_key = secret.get_content(refresh=True)["private-key"]
         return PrivateKey.from_string(private_key)
 
-    def _generate_private_key(self) -> None:
+    def _ensure_private_key(self) -> None:
+        """Make sure there is a private key to be used.
+
+        It will make sure there is a private key passed by the charm using the private_key
+        parameter or generate a new one otherwise.
+        """
+        # Remove the generated private key
+        # if one has been passed by the charm using the private_key parameter
+        if self._private_key:
+            self._remove_private_key_secret()
+            return
         if self._private_key_generated():
+            logger.debug("Private key already generated")
             return
-        private_key = generate_private_key()
-        self.charm.unit.add_secret(
-            content={"private-key": str(private_key)},
-            label=self._get_private_key_secret_label(),
-        )
-        logger.info("Private key generated")
+        self._generate_private_key()
 
     def regenerate_private_key(self) -> None:
         """Regenerate the private key.
 
         Generate a new private key, remove old certificate requests and send new ones.
+
+        Raises:
+            TLSCertificatesError: If the private key is passed by the charm using the
+                private_key parameter.
         """
+        if self._private_key:
+            raise TLSCertificatesError(
+                "Private key is passed by the charm through the private_key parameter, "
+                "this function can't be used"
+            )
         if not self._private_key_generated():
             logger.warning("No private key to regenerate")
             return
-        self._regenerate_private_key()
+        self._generate_private_key()
         self._cleanup_certificate_requests()
         self._send_certificate_requests()
 
-    def _regenerate_private_key(self) -> None:
-        secret = self.charm.model.get_secret(label=self._get_private_key_secret_label())
-        secret.set_content({"private-key": str(generate_private_key())})
-        secret.get_content(refresh=True)
+    def _generate_private_key(self) -> None:
+        """Generate a new private key and store it in a secret.
+
+        This is the case when the private key used is generated by the library.
+            and not passed by the charm using the private_key parameter.
+        """
+        self._store_private_key_in_secret(generate_private_key())
+        logger.info("Private key generated")
 
     def _private_key_generated(self) -> bool:
+        """Check if a private key is stored in a secret.
+
+        This is the case when the private key used is generated by the library.
+        This should not exist when the private key used
+            is passed by the charm using the private_key parameter.
+        """
         try:
-            self.charm.model.get_secret(label=self._get_private_key_secret_label())
-        except (SecretNotFoundError, KeyError):
+            secret = self.charm.model.get_secret(label=self._get_private_key_secret_label())
+            secret.get_content(refresh=True)
+            return True
+        except SecretNotFoundError:
             return False
-        return True
+
+    def _store_private_key_in_secret(self, private_key: PrivateKey) -> None:
+        try:
+            secret = self.charm.model.get_secret(label=self._get_private_key_secret_label())
+            secret.set_content({"private-key": str(private_key)})
+        except SecretNotFoundError:
+            self.charm.unit.add_secret(
+                content={"private-key": str(private_key)},
+                label=self._get_private_key_secret_label(),
+            )
+
+    def _remove_private_key_secret(self) -> None:
+        """Remove the private key secret."""
+        try:
+            secret = self.charm.model.get_secret(label=self._get_private_key_secret_label())
+            secret.remove_all_revisions()
+        except SecretNotFoundError:
+            logger.warning("Private key secret not found, nothing to remove")
 
     def _csr_matches_certificate_request(
         self, certificate_signing_request: CertificateSigningRequest, is_ca: bool
@@ -1429,9 +1511,9 @@ def _tls_relation_created(self) -> bool:
 
     def _get_private_key_secret_label(self) -> str:
         if self.mode == Mode.UNIT:
-            return f"{LIBID}-private-key-{self._get_unit_number()}"
+            return f"{LIBID}-private-key-{self._get_unit_number()}-{self.relationship_name}"
         elif self.mode == Mode.APP:
-            return f"{LIBID}-private-key"
+            return f"{LIBID}-private-key-{self.relationship_name}"
         else:
             raise TLSCertificatesError("Invalid mode. Must be Mode.UNIT or Mode.APP.")