How do you use an HTTP/HTTPS proxy with boto3?

Question

As of at least version 1.5.79, botocore accepts a proxies argument in the botocore config.

e.g.

import boto3
from botocore.config import Config

boto3.resource('s3', config=Config(proxies={'https': 'foo.bar:3128'}))

boto3 resource
https://boto3.readthedocs.io/en/latest/reference/core/session.html#boto3.session.Session.resource

botocore config
https://botocore.readthedocs.io/en/stable/reference/config.html#botocore.config.Config