Fallback to pure-python RSA failing (when Cryptography is not available)

[JavaWiz1]

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• Search the issues already opened: https://github.com/googleapis/google-auth-library-python/issues

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Environment details

• OS: Windows 11
• Python version: 3.8
• pip version: n/a
• google-auth version: 2.14.1

Steps to reproduce

1. Running in Kodi, no Cryptography package available

Fails on import of rsa module (see stacktrace below)

=======================
I believe there are 2 fixes necessary:

1. google.auth.crypt.rsa.py - modify except statement to include ModuleNotFoundError
   from:

try: 
    # Prefer cryptograph-based RSA implementation.
    from google.auth.crypt import _cryptography_rsa

    RSASigner = _cryptography_rsa.RSASigner
    RSAVerifier = _cryptography_rsa.RSAVerifier
except ImportError:  # praga: NO COVER
    # Fallback to pure-python RSA implementation if cryptography is
...

to

try: 
    # Prefer cryptograph-based RSA implementation.
    from google.auth.crypt import _cryptography_rsa

    RSASigner = _cryptography_rsa.RSASigner
    RSAVerifier = _cryptography_rsa.RSAVerifier
except (ImportError, ModuleNotFoundError):  # praga: NO COVER
    # Fallback to pure-python RSA implementation if cryptography is
...

2. in google.auth.crypt._python_rsa.py, fully qualify import for rsa module

from

import rsa  # type: ignore

to

import google.auth.crypt.rsa  # type: ignore

Stack Trace: of issue:

Error Type: <class 'ModuleNotFoundError'>
Error Contents: No module named 'rsa'
Traceback (most recent call last):
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-library\lib\google\auth\crypt\rsa.py", line 20, in <module>
   from google.auth.crypt import _cryptography_rsa
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-library\lib\google\auth\crypt\_cryptography_rsa.py", line 22, in <module>
   import cryptography.exceptions
ModuleNotFoundError: No module named 'cryptography'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\plugin.video.arloview\default.py", line 8, in <module>
   from resources.lib import arlo_stream
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\plugin.video.arloview\resources\lib\arlo_stream.py", line 10, in <module>
   import arlo
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.arlo\lib\arlo.py", line 48, in <module>
   from google_auth_oauthlib.flow import InstalledAppFlow
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-oauthlib\lib\google_auth_oauthlib\__init__.py", line 21, in <module>
   from .interactive import get_user_credentials
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-oauthlib\lib\google_auth_oauthlib\interactive.py", line 27, in <module>
   import google_auth_oauthlib.flow
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-oauthlib\lib\google_auth_oauthlib\flow.py", line 66, in <module>
   import google.auth.transport.requests
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-library\lib\google\auth\transport\requests.py", line 48, in <module>
   from google.oauth2 import service_account
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-library\lib\google\oauth2\service_account.py", line 77, in <module>
   from google.auth import _service_account_info
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-library\lib\google\auth\_service_account_info.py", line 22, in <module>
   from google.auth import crypt
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-library\lib\google\auth\crypt\__init__.py", line 43, in <module>
   from google.auth.crypt import rsa
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-library\lib\google\auth\crypt\rsa.py", line 27, in <module>
   from google.auth.crypt import _python_rsa
 File "C:\Users\a_dam\AppData\Roaming\Kodi\addons\script.module.google-auth-library\lib\google\auth\crypt\_python_rsa.py", line 28, in <module>
   import rsa  # type: ignore
ModuleNotFoundError: No module named 'rsa'

Making sure to follow these steps will guarantee the quickest resolution possible.

Thanks!