cryptography int_from_bytes is deprecated

[jgriffith-cp]

Error: CryptographyDeprecationWarning: int_from_bytes is deprecated, use int.from_bytes instead

google-auth-library-python/google/auth/crypt/es256.py

Line 56 in 77d7f1b

r = utils.int_from_bytes(sig_bytes[:32], byteorder="big")

Environment details

• OS: Ubuntu 20.04.3
• Python version: 3.8.10
• pip version: 20.0.2
• google-auth version: 2.3.2

Steps to reproduce

1. install google auth using pip
2. Python: from google.oauth2 import service_account

[busunkim96]

@arithmetic1728 I think this got re-added with the 2.7 re-shuffle for gcloud. Can the logic be adjusted so Python 3 users don't see the deprecating warning? (original fix was in #846 and #848)