PYTHON-3474 Improve documentation about credential handling (#1080)

Author: blink1073

doc/changelog.rst

@@ -1,8 +1,11 @@
 Changelog
 =========
 
-Changes in Version 4.3
-----------------------
+Changes in Version 4.3 (4.3.2)
+------------------------------
+
+Note: We withheld uploading tags 4.3.0 and 4.3.1 to PyPI due to a
+version handling error and a necessary documentation update.
 
 `dnspython <https://pypi.python.org/pypi/dnspython>`_ is now a required
 dependency. This change makes PyMongo easier to install for use with "mongodb+srv://"

doc/examples/authentication.rst

@@ -268,11 +268,12 @@ or the local EC2 or ECS endpoint. The order in which the client searches for
 when using ``pymongo_auth_aws>=1.1.0``.
 
 Because we are now using ``boto3`` to handle credentials, the order and
-locations of credentials are slightly different from previous versions.
-Particularly, if you have a shared AWS credentials or config file,
+locations of credentials are slightly different from before.  Particularly,
+if you have a shared AWS credentials or config file,
 then those credentials will be used by default if AWS auth environment
-variables are not set.  To override this behavior, set ``AWS_PROFILE=""`` in
-your shell or add ``os.environ["AWS_PROFILE"] = ""`` to your script or
+variables are not set.  To override this behavior, set
+``AWS_SHARED_CREDENTIALS_FILE=""`` in your shell or add
+``os.environ["AWS_SHARED_CREDENTIALS_FILE"] = ""`` to your script or
 application.  Alternatively, you can create an AWS profile specifically for
 your MongoDB credentials and set ``AWS_PROFILE`` to that profile name.