Mssparkutils.credentials.getSecretWithLS to get Certificate and create CertificateCredential in Synapse

@BEPV

Thanks for the question and using MS Q&A platform.

The issue you're encountering with base64.b64decode likely stems from the fact that PKCS12 certificates contain not just the certificate itself, but also the private key and other information. Base64 decoding is meant for text data, and the PKCS12 format isn't simply encoded text.

Here's how you can correctly handle the PKCS12 certificate and create a CertificateCredential in Synapse Workspace:

import base64
from cryptography.hazmat.primitives.serialization import pkcs12
from cryptography.hazmat.primitives import hashes, serialization
def create_certificate_credential(linked_service_name, cert_name, tenant_id, client_id):
  """
  Reads a PKCS12 certificate from Key Vault using mssparkutils and creates a CertificateCredential.
  Args:
      linked_service_name (str): Name of the Linked Service that accesses Key Vault.
      cert_name (str): Name of the secret in Key Vault containing the PKCS12 certificate.
      tenant_id (str): Azure tenant ID.
      client_id (str): Client ID (application ID) of your service principal.
  Returns:
      azure.identity.CertificateCredential: The created CertificateCredential object.
  """
  # Retrieve the PKCS12 data from Key Vault using mssparkutils
  certificate_data = mssparkutils.credentials.getSecretWithLS(linked_service_name, cert_name)
  # Load the PKCS12 data using cryptography library
  private_key, certificate, additional_certificates = pkcs12.load_key_and_certificates(certificate_data, None)
  # You don't need to base64 decode the PKCS12 data
  return CertificateCredential(tenant_id=tenant_id, client_id=client_id, certificate_data=certificate_data)
# Example usage
credential = create_certificate_credential(linked_service_name="myKeyVaultLS", cert_name="myCert", tenant_id="your-tenant-id", client_id="your-client-id")

This code snippet addresses the following points:

1. Import Libraries: Imports necessary libraries for PKCS12 handling (cryptography).
2. Function Definition: Defines a function create_certificate_credential that takes relevant parameters.
3. Retrieve PKCS12 Data: Retrieves the PKCS12 data using mssparkutils.credentials.getSecretWithLS.
4. Load PKCS12 Data: Uses cryptography.hazmat.primitives.serialization.pkcs12.load_key_and_certificates to extract the private key and certificate from the PKCS12 data.
5. Create CertificateCredential: Creates the CertificateCredential object directly using the retrieved certificate_data (no base64 decoding needed).
6. Example Usage: Demonstrates how to call the function with your specific details.

By using the cryptography library and avoiding base64 decoding of the entire PKCS12 data, you can correctly create a CertificateCredential object for use in Synapse Workspace.

Hope this helps. Do let us know if you any further queries.

I also tried that approach but when I pass the certificate from the KeyVault directly to the CertificateCredential I am getting the following error message:

    157         password = password.encode("utf-8")

    158 password = cast("Optional[bytes]", password)

--> 160 if b"-----BEGIN" in certificate_data:

    161     cert = load_pem_certificate(certificate_data, password)

    162 else:

TypeError: 'in <string>' requires string as left operand, not bytes

@BEPV

The error message "TypeError: 'in <string>' requires string as left operand, not bytes" indicates that the in operator is being used with a byte string (certificate_data) instead of a regular string. This is happening in the if b"-----BEGIN" line of your code.

Here's how to fix the issue based on the previous response and the new error message:

Solution:

1. Decode the certificate data before checking for the PEM header:

      if "-----BEGIN" in certificate_data.decode("utf-8"):
          # ... rest of your code for loading PEM certificate
      else:
          # Handle non-PEM certificate format (if applicable)
   

This decodes the certificate_data (which is assumed to be bytes) into a string using UTF-8 encoding. Then, the in operator can be used correctly to check for the presence of the PEM header within the decoded string.

Explanation:

• The in operator is designed to work with strings, not byte strings. Decoding the byte string allows for string comparison using in.
• Decoding with UTF-8 encoding assumes the certificate data is encoded in that format. If you know the specific encoding used, adjust accordingly.

That solution is still not working , the certificate is not a string and does not have attribute to decode, the certificate is in PKCS #12 format, this is not a PEM file, not sure if that is causing the error.

Here is my code with your last suggestion:

certificate_data = mssparkutils.credentials.getSecretWithLS(linked_service_name, 'cert')
certificate_decode = certificate_data.decode("utf-8")
credential =  CertificateCredential(tenant_id=tenant_id, client_id=service_principal_id, certificate_data=certificate_decode)

Here is the output error message:

AttributeError                            Traceback (most recent call last)
Cell In [27], line 15
14 certificate_data = mssparkutils.credentials.getSecretWithLS(linked_service_name, 'cert')
---> 15 certificate_decode = certificate_data.decode("utf-8")
17 credential =  CertificateCredential(tenant_id=tenant_id, client_id=service_principal_id, certificate_data=certificate_decode)

AttributeError: 'str' object has no attribute 'decode'

@BEPV The error message 'str' object has no attribute 'decode' indicates that certificate_data is already a string, so you don’t need to decode it.

However, the CertificateCredential expects the certificate_data argument to be bytes, not a string. If your certificate_data is a base64-encoded string, you should decode it back into bytes before passing it to CertificateCredential. Here’s how you can do it:

import base64
certificate_data = mssparkutils.credentials.getSecretWithLS(linked_service_name, 'cert')
certificate_bytes = base64.b64decode(certificate_data)
credential = CertificateCredential(tenant_id=tenant_id, client_id=service_principal_id, certificate_data=certificate_bytes)

This code first retrieves the certificate data from your linked service, then decodes the base64 string into bytes using base64.b64decode(), and finally creates the CertificateCredential with the byte data