# ------------------------------------
# Copyright (c) Microsoft Corporation.
# Licensed under the MIT License.
# ------------------------------------
from binascii import hexlify
from typing import cast, NamedTuple, Union, Dict, Any, Optional
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
from .._internal import validate_tenant_id
from .._internal.client_credential_base import ClientCredentialBase
[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
`Microsoft Entra ID documentation
<https://learn.microsoft.com/entra/identity-platform/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 a Microsoft Entra 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
:keyword bool disable_instance_discovery: Determines whether or not instance discovery is performed when attempting
to authenticate. Setting this to true will completely disable both instance discovery and authority validation.
This functionality is intended for use in scenarios where the metadata endpoint cannot be reached, such as in
private clouds or Azure Stack. The process of instance discovery entails retrieving authority metadata from
https://login.microsoft.com/ to validate the authority. By setting this to **True**, the validation of the
authority is disabled. As a result, it is crucial to ensure that the configured authority host is valid and
trustworthy.
:keyword List[str] additionally_allowed_tenants: Specifies tenants in addition to the specified "tenant_id"
for which the credential may acquire tokens. Add the wildcard value "*" to allow the credential to
acquire tokens for any tenant the application can access.
.. admonition:: Example:
.. literalinclude:: ../samples/credential_creation_code_snippets.py
:start-after: [START create_certificate_credential]
:end-before: [END create_certificate_credential]
:language: python
:dedent: 4
:caption: Create a CertificateCredential.
"""
def __init__(self, tenant_id: str, client_id: str, certificate_path: Optional[str] = None, **kwargs: 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: bytes) -> bytes:
"""Extract a certificate chain from a PEM file's bytes, removing line breaks.
:param bytes pem_bytes: The PEM file's bytes
:return: The certificate chain
:rtype: bytes
"""
# 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: bytes, password: Optional[bytes] = None) -> _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: bytes, password: Optional[bytes] = None) -> _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
raise ValueError("Failed to deserialize certificate in PEM or PKCS12 format") from 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: Optional[str] = None,
password: Optional[Union[bytes, str]] = None,
certificate_data: Optional[bytes] = None,
send_certificate_chain: bool = False,
**_: Any
) -> Dict:
"""Load a certificate from a filesystem path or bytes, return it as a dict suitable for msal.ClientApplication.
:param str certificate_path: Path to a PEM or PKCS12 certificate file.
:param bytes password: The certificate's password, if any.
:param bytes certificate_data: The PEM or PKCS12 certificate's bytes.
:param bool send_certificate_chain: Whether to send the certificate chain. Defaults to False.
:return: The certificate as a dict
:rtype: dict
"""
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, no need to encode.
if isinstance(password, str):
password = password.encode("utf-8")
password = cast("Optional[bytes]", password)
if b"-----BEGIN" in certificate_data:
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"] = chain.decode("utf-8")
except ValueError as ex:
# we shouldn't land here--cryptography already loaded the cert and would have raised if it were malformed
raise ValueError("Malformed certificate") from ex
return client_credential