Implement Refreshable Chained AWS Session for Multi-Account Role Assumption

[sgandhi1311]

Overview

This PR introduces functionality to establish a chained AWS session for multi-account role assumption, allowing the system to:

1. Assume a role in a proxy account and use the resulting credentials.
2. Use the proxy session to assume a secondary role in a customer account.
3. Automatically refresh both sessions upon expiration using RefreshableCredentials to maintain seamless, uninterrupted access.

Context

Due to the requirement to perform operations in a customer account by first assuming a role in an intermediate (proxy) account, this chained session approach enables:

• Session Reuse: Enables reusing a single session across AWS services.
• Automatic Refreshing: Ensures that both sessions are refreshed as needed, avoiding disruptions during operations.

Implementation Details

1. Primary Role Assumption (Proxy Account):

   • Utilizes AssumeRoleCredentialFetcher to assume a role in Proxy.
   • RefreshableCredentials is used to enable automatic refreshing on expiration.
   • This session is cached to avoid redundant calls and improve performance.

2. Chained Role Assumption (Customer Account):

   • Leverages the proxy account session to assume a role in Customer.
   • A second AssumeRoleCredentialFetcher is set up with RefreshableCredentials to automatically refresh upon expiry.

3. Default Session Setup for boto3:

   • Configures boto3 to use this chained session, so all AWS API calls automatically utilize the assumed roles without additional configuration.
   • Logs the current session expiration timestamp to verify that refreshing occurs as expected.

Example Usage

The setup function initializes the chained session, and subsequent boto3 clients can be created without additional steps. Here’s a usage example:

config = {
    'proxy_account_id': '123456789012',
    'proxy_role_name': 'ProxyRole',
    'account_id': '987654321098',
    'role_name': 'CustomerRole',
    'proxy_external_id': 'ProxyExternalID',
    'external_id': 'CustomerExternalID',
    'region': 'us-east-1'
}

setup_aws_client(config)
s3_client = boto3.client('s3')
# Use s3_client for S3 operations, with credentials refreshing automatically