fix(google-auth): add gRPC extra and clean up obsolete TODOs (#17644)

- Added `grpc` extra (`"grpc": ["grpcio"]`) and updated
`testing_extra_require` to use `*grpc_extra_require`.
- Removed obsolete TODO comments for `grpcio`, `oauth2client`, and
`urllib3` bounds.

Fixes #1735
Fixes #1736
Fixes #1739

Author: ohmayr

packages/google-auth/setup.py

@@ -42,10 +42,14 @@
 
 rsa_extra_require = ["rsa>=3.1.4,<5"]
 
+grpc_extra_require = [
+    "grpcio >= 1.59.0, < 2.0.0; python_version < '3.14'",
+    "grpcio >= 1.75.1, < 2.0.0; python_version >= '3.14'",
+]
+
 # Unit test requirements.
 testing_extra_require = [
-    # TODO(https://github.com/googleapis/google-auth-library-python/issues/1735): Remove `grpcio` from testing requirements once an extra is added for `grpcio` dependency.
-    "grpcio",
+    *grpc_extra_require,
     "flask",
     "freezegun",
     *pyjwt_extra_require,
@@ -74,8 +78,7 @@
     "testing": testing_extra_require,
     "urllib3": urllib3_extra_require,
     "rsa": rsa_extra_require,
-    # TODO(https://github.com/googleapis/google-auth-library-python/issues/1735): Add an extra for `grpcio` dependency.
-    # TODO(https://github.com/googleapis/google-auth-library-python/issues/1736): Add an extra for `oauth2client` dependency.
+    "grpc": grpc_extra_require,
 }
 
 with io.open("README.rst", "r") as fh:

packages/google-auth/testing/constraints-3.10.txt

@@ -10,4 +10,5 @@ setuptools==40.3.0
 cryptography==38.0.3
 aiohttp==3.8.0
 requests==2.20.0
-pyjwt==2.0
+pyjwt==2.0
+grpcio==1.59.0