# ------------------------------------
# Copyright (c) Microsoft Corporation.
# Licensed under the MIT License.
# ------------------------------------
from binascii import hexlify
from typing import cast, NamedTuple, TYPE_CHECKING
from cryptography import x509
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric.rsa import RSAPrivateKey
from cryptography.hazmat.backends import default_backend
import six
from .._internal import validate_tenant_id
from .._internal.client_credential_base import ClientCredentialBase
if TYPE_CHECKING:
# pylint:disable=ungrouped-imports
from typing import Any, Optional, Union
[docs]class CertificateCredential(ClientCredentialBase):
"""Authenticates as a service principal using a certificate.
The certificate must have an RSA private key, because this credential signs assertions using RS256. See
`Azure Active Directory documentation
<https://docs.microsoft.com/azure/active-directory/develop/active-directory-certificate-credentials#register-your-certificate-with-microsoft-identity-platform>`_
for more information on configuring certificate authentication.
:param str tenant_id: ID of the service principal's tenant. Also called its "directory" ID.
:param str client_id: the service principal's client ID
:param str certificate_path: Optional path to a certificate file in PEM or PKCS12 format, including the private
key. If not provided, **certificate_data** is required.
:keyword str authority: Authority of an Azure Active Directory endpoint, for example "login.microsoftonline.com",
the authority for Azure Public Cloud (which is the default). :class:`~azure.identity.AzureAuthorityHosts`
defines authorities for other clouds.
:keyword bytes certificate_data: the bytes of a certificate in PEM or PKCS12 format, including the private key
:keyword password: The certificate's password. If a unicode string, it will be encoded as UTF-8. If the certificate
requires a different encoding, pass appropriately encoded bytes instead.
:paramtype password: str or bytes
:keyword bool send_certificate_chain: if True, the credential will send the public certificate chain in the x5c
header of each token request's JWT. This is required for Subject Name/Issuer (SNI) authentication. Defaults to
False.
:keyword cache_persistence_options: configuration for persistent token caching. If unspecified, the credential
will cache tokens in memory.
:paramtype cache_persistence_options: ~azure.identity.TokenCachePersistenceOptions
"""
def __init__(self, tenant_id, client_id, certificate_path=None, **kwargs):
# type: (str, str, Optional[str], **Any) -> None
validate_tenant_id(tenant_id)
client_credential = get_client_credential(certificate_path, **kwargs)
super(CertificateCredential, self).__init__(
client_id=client_id, client_credential=client_credential, tenant_id=tenant_id, **kwargs
)
def extract_cert_chain(pem_bytes):
# type: (bytes) -> bytes
"""Extract a certificate chain from a PEM file's bytes, removing line breaks."""
# if index raises ValueError, there's no PEM-encoded cert
start = pem_bytes.index(b"-----BEGIN CERTIFICATE-----")
footer = b"-----END CERTIFICATE-----"
end = pem_bytes.rindex(footer)
chain = pem_bytes[start : end + len(footer) + 1]
return b"".join(chain.splitlines())
_Cert = NamedTuple("_Cert", [("pem_bytes", bytes), ("private_key", "Any"), ("fingerprint", bytes)])
def load_pem_certificate(certificate_data, password):
# type: (bytes, Optional[bytes]) -> _Cert
private_key = serialization.load_pem_private_key(certificate_data, password, backend=default_backend())
cert = x509.load_pem_x509_certificate(certificate_data, default_backend())
fingerprint = cert.fingerprint(hashes.SHA1()) # nosec
return _Cert(certificate_data, private_key, fingerprint)
def load_pkcs12_certificate(certificate_data, password):
# type: (bytes, Optional[bytes]) -> _Cert
from cryptography.hazmat.primitives.serialization import Encoding, NoEncryption, pkcs12, PrivateFormat
try:
private_key, cert, additional_certs = pkcs12.load_key_and_certificates(
certificate_data, password, backend=default_backend()
)
except ValueError as ex:
# mentioning PEM here because we raise this error when certificate_data is garbage
six.raise_from(ValueError("Failed to deserialize certificate in PEM or PKCS12 format"), ex)
if not private_key:
raise ValueError("The certificate must include its private key")
if not cert:
raise ValueError("Failed to deserialize certificate in PEM or PKCS12 format")
# This serializes the private key without any encryption it may have had. Doing so doesn't violate security
# boundaries because this representation of the key is kept in memory. We already have the key and its
# password, if any, in memory.
key_bytes = private_key.private_bytes(Encoding.PEM, PrivateFormat.PKCS8, NoEncryption())
pem_sections = [key_bytes] + [c.public_bytes(Encoding.PEM) for c in [cert] + additional_certs]
pem_bytes = b"".join(pem_sections)
fingerprint = cert.fingerprint(hashes.SHA1()) # nosec
return _Cert(pem_bytes, private_key, fingerprint)
def get_client_credential(certificate_path, password=None, certificate_data=None, send_certificate_chain=False, **_):
# type: (Optional[str], Optional[Union[bytes, str]], Optional[bytes], bool, **Any) -> dict
"""Load a certificate from a filesystem path or bytes, return it as a dict suitable for msal.ClientApplication"""
if certificate_path:
if certificate_data:
raise ValueError('Please specify either "certificate_path" or "certificate_data", not both')
with open(certificate_path, "rb") as f:
certificate_data = f.read()
elif not certificate_data:
raise ValueError('CertificateCredential requires a value for either "certificate_path" or "certificate_data"')
if password:
# if password is already bytes, this won't change its encoding
password = six.ensure_binary(password, "utf-8")
password = cast("Optional[bytes]", password)
if certificate_data.startswith(b"-----"):
cert = load_pem_certificate(certificate_data, password)
else:
cert = load_pkcs12_certificate(certificate_data, password)
password = None # load_pkcs12_certificate returns cert.pem_bytes decrypted
if not isinstance(cert.private_key, RSAPrivateKey):
raise ValueError("The certificate must have an RSA private key because RS256 is used for signing")
client_credential = {"private_key": cert.pem_bytes, "thumbprint": hexlify(cert.fingerprint).decode("utf-8")}
if password:
client_credential["passphrase"] = password
if send_certificate_chain:
try:
# the JWT needs the whole chain but load_pem_x509_certificate deserializes only the signing cert
chain = extract_cert_chain(cert.pem_bytes)
client_credential["public_certificate"] = six.ensure_str(chain)
except ValueError as ex:
# we shouldn't land here--cryptography already loaded the cert and would have raised if it were malformed
six.raise_from(ValueError("Malformed certificate"), ex)
return client_credential