Owen Rumney

Software Engineer

In a recent post I covered an using RefreshingAWSCredentials within .NET AWS SDK to solve an issue with the way my current organisation has configured SingleSignOn (SSO) and temporary credentials.

Essentially, the solution involves a background process updating a credenial file then using a time limited AWSCredential object to refresh the credentials.


The next issue to surface was satisfying the same requirement but for the Python based component of the 3rd party solution.

Refreshing Credential File

In this case, on RedHat instance, there is a cron job executing a Python script which handles the SSO process and writes the updated credentials and session token to a file which can be used by the 3rd party component.

Refreshing the Credentials in code

The exising code creates a session then creates the required resources. This works fine for the first hour till the temporary credentials expire.

from botocore.session import get_session

queues['incoming'] = session.resource('sqs', region).get_queue_by_name(QueueName='incoming_queue')

There is only a small amount of work to make this refreshing against the externally updated credential file. For this we’ll make use of the RefreshableCredentials from botocore.credentials.

from botocore.credentials import RefreshableCredentials
from botocore.session import get_session
from configparser import ConfigParser
from datetime import datetime, timedelta, timezone

def refresh_external_credentials():
    config = ConfigParser()
    profile = config.get(profile_name)
    expiry = (datetime.now(timezone.utc) + timedelta(minutes=refresh_minutes))
    return {
        "access_key": profile.get('aws_access_key_id'),
        "secret_key": profile.get('aws_secret_access_key'),
        "token": profile.get('aws_session_token'),
        "expiry_time": expiry.isoformat()

There are a few config entries here.

  • credential_file_path is the location of the credential file that is getting externally updated
  • profile_name is the profile in the credential file that you want to use
  • refresh_minutes is the time before the AWS credential will expire and the refresh_external_credentials() function will get called.

We now need to create the credential object for a session which will then be able to auto refresh.

session_credentials = RefreshableCredentials.create_from_metadata(
    metadata = refresh_external_credentials(),
    refresh_using = refresh_external_credentials,
    method = 'sts-assume-role'

Going back to the original code, the new session_credentials can be plugged in to provide long life application against temporary tokens.

import boto3

# ideally taken from config
region = 'eu-west-1'
incoming_queue_name = 'incoming_queue'

session = get_session()
session._credentials = session_credentials
autorefresh_session = boto3.Session(botocore_session=session)

queues['incoming'] = autorefresh_session.resource('sqs', region).get_queue_by_name(QueueName=incoming_queue_name)