boto3.resource to create S3 resource fails when proxies config is used

[GururajKheni]

session = boto3.Session(profile_name="default")

sts = session.client("sts")
response = sts.assume_role(
    RoleArn=assume_role_arn,
    RoleSessionName=session_name)

s3_resource = boto3.resource('s3', aws_access_key_id=response['Credentials']['AccessKeyId'],
                             aws_secret_access_key=response['Credentials']['SecretAccessKey'],
                             aws_session_token=response['Credentials']['SessionToken'],
                             config=Config(proxies={'https': 'http://proxy.server.co.uk:8080'}))

This fails with error
EndpointConnectionError: Could not connect to the endpoint URL: "https://sts.amazonaws.com/"

I made sure my aws config and credentials are properly set and working because if I set proxy server details as env variable then everything works fine

# Set proxy servers as environment variables
os.environ['HTTP_PROXY'] = PURPLE_HTTP_PROXY
os.environ['HTTPS_PROXY'] = PURPLE_HTTP_PROXY

s3_resource = boto3.resource('s3', aws_access_key_id=response['Credentials']['AccessKeyId'],
                             aws_secret_access_key=response['Credentials']['SecretAccessKey'],
                             aws_session_token=response['Credentials']['SessionToken'])

This works fine.

Note: I am running these calls in a container with firewall restrictions, that's the reason I need to use proxy config