Silent dependency on urllib3 in _aiohttp_requests

[asafflesch]

Environment details

• OS: OSX, Linux
• Python version: 3.7
• pip version:
• google-auth version: 1.24.0

Steps to reproduce

1. Setup a clean virtualenv
2. pip install google-auth==1.24.0 aiohttp==3.5.4 (version I happen to be using)
3. Run "from google.auth.transport import _aiohttp_requests" in a python3 session

You should get a ModuleNotFoundError for "urllib3"

[asafflesch]

(I see there's also a silent dependency there on requests - maybe you just intend for the exception on requests not being installed to go off first?)

[busunkim96]

Hey @Faqa,

Before aiohttp_requests we didn't have urllib3 or requests as hard dependencies and assumed that folks would install one or both as needed after seeing one of these error messages:

google-auth-library-python/google/auth/transport/requests.py

Lines 25 to 35 in 65074d3

	try:
	import requests
	except ImportError as caught_exc: # pragma: NO COVER
	import six
	six.raise_from(
	ImportError(
	"The requests library is not installed, please install the "
	"requests package to use the requests transport."
	),
	caught_exc,

google-auth-library-python/google/auth/transport/urllib3.py

Lines 34 to 45 in 65074d3

	try:
	import urllib3
	except ImportError as caught_exc: # pragma: NO COVER
	import six
	six.raise_from(
	ImportError(
	"The urllib3 library is not installed, please install the "
	"urllib3 package to use the urllib3 transport."
	),
	caught_exc,
	)

Since _aiohttp_requests has a hard dependency on both I think we should just add it to the aiohttp extra to reduce friction. I'll open a PR adjusting the extras. After that change if you do pip install google-auth[aiohttp] it should pull in all the required dependencies.

google-auth-library-python/setup.py

Lines 32 to 35 in 65074d3

	extras = {
	"aiohttp": "aiohttp >= 3.6.2, < 4.0.0dev; python_version>='3.6'",
	"pyopenssl": "pyopenssl>=20.0.0",
	}

[parthea]

@busunkim96 Please can you take a look?