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"""
This module contains Azure Key Vault Backend.
.. spelling:word-list::
Entra
"""
from __future__ import annotations
import logging
import os
import re
from functools import cached_property
from azure.core.exceptions import ResourceNotFoundError
from azure.identity import ClientSecretCredential, DefaultAzureCredential
from azure.keyvault.secrets import SecretClient
from airflow.providers.microsoft.azure.utils import get_sync_default_azure_credential
from airflow.secrets import BaseSecretsBackend
from airflow.utils.log.logging_mixin import LoggingMixin
[docs]
class AzureKeyVaultBackend(BaseSecretsBackend, LoggingMixin):
"""
Retrieves Airflow Connections or Variables from Azure Key Vault secrets.
The Azure Key Vault can be configured as a secrets backend in the ``airflow.cfg``:
.. code-block:: ini
[secrets]
backend = airflow.providers.microsoft.azure.secrets.key_vault.AzureKeyVaultBackend
backend_kwargs = {"connections_prefix": "airflow-connections", "vault_url": "<azure_key_vault_uri>"}
For example, if the secrets prefix is ``airflow-connections-smtp-default``, this would be accessible
if you provide ``{"connections_prefix": "airflow-connections"}`` and request conn_id ``smtp-default``.
And if variables prefix is ``airflow-variables-hello``, this would be accessible
if you provide ``{"variables_prefix": "airflow-variables"}`` and request variable key ``hello``.
For client authentication, the ``DefaultAzureCredential`` from the Azure Python SDK is used as
credential provider, which supports service principal, managed identity and user credentials
For example, to specify a service principal with secret you can set the environment variables
``AZURE_TENANT_ID``, ``AZURE_CLIENT_ID`` and ``AZURE_CLIENT_SECRET``.
.. seealso::
For more details on client authentication refer to the ``DefaultAzureCredential`` Class reference:
https://docs.microsoft.com/en-us/python/api/azure-identity/azure.identity.defaultazurecredential?view=azure-python
:param connections_prefix: Specifies the prefix of the secret to read to get Connections
If set to None (null), requests for connections will not be sent to Azure Key Vault
:param variables_prefix: Specifies the prefix of the secret to read to get Variables
If set to None (null), requests for variables will not be sent to Azure Key Vault
:param config_prefix: Specifies the prefix of the secret to read to get Variables.
If set to None (null), requests for configurations will not be sent to Azure Key Vault
:param vault_url: The URL of an Azure Key Vault to use
:param sep: separator used to concatenate secret_prefix and secret_id. Default: "-"
:param tenant_id: The tenant id of an Azure Key Vault to use.
If not given, it falls back to ``DefaultAzureCredential``
:param client_id: The client id of an Azure Key Vault to use.
If not given, it falls back to ``DefaultAzureCredential``
:param managed_identity_client_id: The client ID of a user-assigned managed identity.
If provided with `workload_identity_tenant_id`, they'll pass to ``DefaultAzureCredential``.
:param workload_identity_tenant_id: ID of the application's Microsoft Entra tenant.
Also called its "directory" ID.
If provided with `managed_identity_client_id`, they'll pass to ``DefaultAzureCredential``.
"""
def __init__(
self,
connections_prefix: str = "airflow-connections",
variables_prefix: str = "airflow-variables",
config_prefix: str = "airflow-config",
vault_url: str = "",
sep: str = "-",
*,
tenant_id: str = "",
client_id: str = "",
client_secret: str = "",
managed_identity_client_id: str = "",
workload_identity_tenant_id: str = "",
**kwargs,
) -> None:
super().__init__()
[docs]
self.vault_url = vault_url
[docs]
self.connections_prefix: str | None
if connections_prefix:
self.connections_prefix = connections_prefix.rstrip(sep)
else:
self.connections_prefix = connections_prefix
[docs]
self.variables_prefix: str | None
if variables_prefix:
self.variables_prefix = variables_prefix.rstrip(sep)
else:
self.variables_prefix = variables_prefix
[docs]
self.config_prefix: str | None
if config_prefix:
self.config_prefix = config_prefix.rstrip(sep)
else:
self.config_prefix = config_prefix
logger = logging.getLogger("azure.core.pipeline.policies.http_logging_policy")
try:
logger.setLevel(os.environ.get("AZURE_HTTP_LOGGING_LEVEL", logging.WARNING))
except ValueError:
logger.setLevel(logging.WARNING)
[docs]
self.tenant_id = tenant_id
[docs]
self.client_id = client_id
[docs]
self.client_secret = client_secret
[docs]
self.managed_identity_client_id = managed_identity_client_id
[docs]
self.workload_identity_tenant_id = workload_identity_tenant_id
@cached_property
[docs]
def client(self) -> SecretClient:
"""Create a Azure Key Vault client."""
credential: ClientSecretCredential | DefaultAzureCredential
if all([self.tenant_id, self.client_id, self.client_secret]):
credential = ClientSecretCredential(self.tenant_id, self.client_id, self.client_secret)
else:
credential = get_sync_default_azure_credential(
managed_identity_client_id=self.managed_identity_client_id,
workload_identity_tenant_id=self.workload_identity_tenant_id,
)
client = SecretClient(vault_url=self.vault_url, credential=credential, **self.kwargs)
return client
[docs]
def get_conn_value(self, conn_id: str, team_name: str | None = None) -> str | None:
"""
Get a serialized representation of Airflow Connection from an Azure Key Vault secret.
:param conn_id: The Airflow connection id to retrieve
:param team_name: Team name associated to the task trying to access the connection (if any)
"""
if self.connections_prefix is None:
return None
if self._names_a_team_namespace(conn_id):
self._log_refusal("connection", conn_id)
return None
return self._get_secret(self.connections_prefix, conn_id, team_name=team_name)
[docs]
def get_variable(self, key: str, team_name: str | None = None) -> str | None:
"""
Get an Airflow Variable from an Azure Key Vault secret.
:param key: Variable Key
:param team_name: Team name associated to the task trying to access the variable (if any)
:return: Variable Value
"""
if self.variables_prefix is None:
return None
if self._names_a_team_namespace(key):
self._log_refusal("variable", key)
return None
return self._get_secret(self.variables_prefix, key, team_name=team_name)
[docs]
def get_config(self, key: str) -> str | None:
"""
Get Airflow Configuration.
:param key: Configuration Option Key
:return: Configuration Option Value
"""
if self.config_prefix is None:
return None
if self._names_a_team_namespace(key):
self._log_refusal("configuration option", key)
return None
return self._get_secret(self.config_prefix, key)
@staticmethod
[docs]
def build_path(path_prefix: str, secret_id: str, sep: str = "-") -> str:
"""
Given a path_prefix and secret_id, build a valid secret name for the Azure Key Vault Backend.
Also replaces underscore in the path with dashes to support easy switching between
environment variables, so ``connection_default`` becomes ``connection-default``.
:param path_prefix: The path prefix of the secret to retrieve
:param secret_id: Name of the secret
:param sep: Separator used to concatenate path_prefix and secret_id
"""
# When an empty prefix is given, do not add a separator to the secret name
if path_prefix == "":
path = f"{secret_id}"
else:
path = f"{path_prefix}{sep}{secret_id}"
return path.replace("_", sep)
def _build_team_secret_name(self, path_prefix: str, team_name: str, secret_id: str) -> str:
"""
Build a team-scoped secret name using a dedicated separator before the secret id.
The secret id is normalised the same way :meth:`build_path` normalises every other name
in this backend. On its own that would let ``b__c`` manufacture the team separator; ids
whose normalised form contains it are refused by the callers before they get here.
"""
team_prefix = self.build_path(path_prefix, team_name, self.sep)
normalized_secret_id = secret_id.replace("_", self.sep)
return f"{team_prefix}{TEAM_SEP}{normalized_secret_id}"
def _names_a_team_namespace(self, secret_id: str) -> bool:
"""
Whether ``secret_id`` spells out a team scoped secret name.
A team scoped secret is named ``<team>{TEAM_SEP}<secret id>``, so an id that itself
contains the team separator makes the built name ambiguous: team ``a`` with id ``b--c``
and team ``a--b`` with id ``c`` produce the same string. Such an id is refused by every
getter -- connections, variables and configuration options, team scoped as well as team
agnostic -- because the ambiguity exists in both directions and the caller's own
namespace is not a safe harbour for it.
The id is never parsed to work out *which* team it names, because it cannot be: nothing
in the string distinguishes the two readings above. Comparing the id against the prefix
the caller's own team builds looks equivalent and is not -- a caller in team ``a`` would
match ``a--b``'s namespace on the prefix and read its secrets. Only the caller's own
namespace is ever constructed, never parsed.
The id is normalised first because :meth:`build_path` maps ``_`` onto the separator
everywhere in this backend, so ``b__c`` reaches Key Vault as ``b--c`` and would
otherwise manufacture the team separator from an id that does not visibly contain it.
"""
return TEAM_SEP in self.build_path("", secret_id, self.sep)
def _log_refusal(self, kind: str, secret_id: str) -> None:
self.log.warning(
"%s id %r resolves to a name containing %r, which separates the team name from the "
"secret id in a team scoped secret name. Such an id is ambiguous and is not looked "
"up. Returning None.",
kind.capitalize(),
secret_id,
TEAM_SEP,
)
def _get_secret(self, path_prefix: str, secret_id: str, team_name: str | None = None) -> str | None:
"""
Get an Azure Key Vault secret value.
:param path_prefix: Prefix for the Path to get Secret
:param secret_id: Secret Key
:param team_name: Team the lookup is scoped to (if any)
"""
# The team scoped name is tried first. Ids that would make it name a namespace other
# than the caller's own are refused by the callers before reaching here.
if team_name:
team_secret = self._get_secret_value(
path_prefix, self._build_team_secret_name("", team_name, secret_id)
)
if team_secret is not None:
return team_secret
return self._get_secret_value(path_prefix, secret_id)
def _get_secret_value(self, path_prefix: str, secret_id: str) -> str | None:
"""Get an Azure Key Vault secret value for the given prefix and key."""
name = self.build_path(path_prefix, secret_id, self.sep)
# Azure Key Vault secret names must be 1-127 characters, containing only 0-9, a-z, A-Z, and -.
# https://learn.microsoft.com/en-us/azure/key-vault/general/about-keys-secrets-certificates#object-identifiers
if not re.fullmatch(r"[0-9a-zA-Z-]{1,127}", name):
self.log.warning(
"Secret name %r is not valid. "
"Azure Key Vault secret names must be 1-127 characters long "
"and contain only alphanumeric characters and dashes.",
name,
)
return None
try:
secret = self.client.get_secret(name=name)
return secret.value
except ResourceNotFoundError as ex:
self.log.debug("Secret %s not found: %s", name, ex)
return None