Environment details

• OS: MacOS 13.5.2
• Python version: 3.9
• pip version: 23.1.2
• google-auth version: 2.22.0

Steps to reproduce

Install cryptography

Run:

import pickle
from google.oauth2 import service_account

credentials = service_account.Credentials.from_service_account_file("credentials.json")

pickle.dumps(credentials)

The object in question seems to be credentials._signer which is either a pickleable pure Python object if cryptography is not installed, or else an unpickleable google.auth.crypt._cryptography_rsa.RSASigner if it is. Specifically, the signer._key object is of type cryptography.hazmat.backends.openssl.rsa._RSAPrivateKey.

This conversation on SO seems related: https://stackoverflow.com/questions/39321606/cant-pickle-an-rsa-key-to-send-over-a-socket

This is impacting the Storage SDK's multiprocessing capability: googleapis/python-storage#1116 despite efforts to work around it.