TestDecryptPrivateKey::test_success fails with pyOpenSSL 24.3.0+

[MeggyCal]

Environment details

• OS: openSUSE Tumbleweed
• Python version: 3.11, 3.12, 3.13
• google-auth version: 2.38.0
• pyOpenSSL version: 25.0.0

Decription

While running the testsuite I encountered a test failure:

[  110s] ______________________ TestDecryptPrivateKey.test_success ______________________
[  110s] 
[  110s] self = <tests.transport.test__mtls_helper.TestDecryptPrivateKey object at 0xf4d69498>
[  110s] 
[  110s]     def test_success(self):
[  110s]         decrypted_key = _mtls_helper.decrypt_private_key(
[  110s]             ENCRYPTED_EC_PRIVATE_KEY, PASSPHRASE_VALUE
[  110s]         )
[  110s]         private_key = crypto.load_privatekey(crypto.FILETYPE_PEM, decrypted_key)
[  110s]         public_key = crypto.load_publickey(crypto.FILETYPE_PEM, EC_PUBLIC_KEY)
[  110s]         x509 = crypto.X509()
[  110s]         x509.set_pubkey(public_key)
[  110s]     
[  110s]         # Test the decrypted key works by signing and verification.
[  110s] >       signature = crypto.sign(private_key, b"data", "sha256")
[  110s] 
[  110s] tests/transport/test__mtls_helper.py:633: 
[  110s] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[  110s] 
[  110s] self = <module 'OpenSSL.crypto' from '/usr/lib/python3.12/site-packages/OpenSSL/crypto.py'>
[  110s] attr = 'sign'
[  110s] 
[  110s]     def __getattr__(self, attr: str) -> object:
[  110s] >       obj = getattr(self._module, attr)
[  110s] E       AttributeError: module 'OpenSSL.crypto' has no attribute 'sign'

Indeed, from pyOpenSSL changelog for 24.3.0:

Removed the deprecated OpenSSL.crypto.sign and OpenSSL.crypto.verify.
cryptography.hazmat.primitives.asymmetric’s signature APIs should be used instead.

Probably it would be best to rewrite the test or better the whole library to cryptography, as recommended by pyOpenSSl.crypto module itself. But I don't really know what I am doing and I am afraid of dinosaurs with laser guns, so please don't expect a PR from me. Could you please think about it? I know it is not a small task.

[MeggyCal]

Initially I tried to patch it and failed (luckily, because I would probably introduce some security issue if I succeeded). But in the process I found a GitHub issue that might come handy: pyca/cryptography#7939.