[Feature]: Support AWS Upstream Authentication

[tharindu1st]

Please select the area the issue is related to

Gateway

Please select the aspect the issue is related to

Aspect/Other (Anything else which does not match above categories)

Suggested Feature

Implement gateway policy to support AWS authentication.

Related Issues

No response

Steps to Verify

• Design Document — A detailed design document has been created and reviewed, covering architecture, data flow, and edge cases.
• Design Mail — A design summary email has been sent to relevant stakeholders for awareness and feedback.
• Code Review — All code changes have been peer-reviewed and approved according to the project's review standards.
• Testing Complete — Adequate unit, integration, and/or end-to-end tests have been written and are passing.
• Documentation Review — User-facing and/or developer documentation has been updated to reflect the new feature and reviewed.
• Feature Complete — The feature is fully implemented, all checklist items above are done, and it is ready for release.