Feature Branch: Add Token Manager

[smithsz]

Checklist

• [x] Tick to sign-off your agreement to the Developer Certificate of Origin (DCO) 1.1
• [x] Added tests for code changes or test/build only changes
• [x] Updated the change log file (CHANGES.md|CHANGELOG.md) or test/build only changes
• [x] Completed the PR template below:

Description

Add new Token Manager for managing authentication tokens.

The manager blocks concurrent token requests. It also preemptively refreshes a token before it expires (dictated by Max-Age).

The Token Manger is used for both Cookie and IAM authentication.

Approach

• Add new TokenManager class (includingCookieTokenManager and IAMTokenManager subclasses).
• Call the manager when requesting an authentication token.

Schema & API Changes

None.

Security and Privacy

None.

Testing

Includes additional unit tests.

Monitoring and Logging

Adds new logging namespaces for TokenManager type classes.