nginx-aws-signature: core library implementation

[shawnhankim]

As an App/API Developer,

I want to quickly implement an application on multiple cloud provider's services (e.g., AWS Lambda, S3, SQS) using a reusable library(nginx-aws-signature) without learning and implementing how to sign API requests. So I can focus on only implementing business logic.

Acceptance Criteria:

• Implement common AWS Signature library by refactoring nginx-s3-gateway.
  • Remove S3 specific logic.
  • Support Signature Version 2 process for the existing services.
  • Support Signature Version 4 process.
• Get temporary security credentials
  • IAM role authentication for service accounts
  • Direct environment variables(e.g. AWS_SESSION_TOKEN) based authentication
• Support NGINX OSS/Plus