Support additional session tags like GITHUB_BASE_REF and GITHUB_EVENT_NAME

[jsimoni]

We'd like to be create a trust document on the AWS Role assumed by GitHub Action workflow that only authorizes a workflow that runs on a pull request that targets a specific branch. In order to do that, we would need this GitHub Action to populate Session Tags with the values in the GITHUB_BASE_REF & GITHUB_EVENT_NAME environmental variables.

https://github.com/aws-actions/configure-aws-credentials#session-tagging

[peterwoodworth]

We should be able to support additional, non-required environment variables as session tags. Thanks for the suggestion!

Documentation here for future reference

[peterwoodworth]

You can currently work around your specific issue through your action configuration like so until we may implement this:

on:
  pull_request_target:
    types:
      - opened
    branches:    
      - 'master'
  push:
    branches:    
      - 'master'

[peterwoodworth]

When we implement this I think the expectation is that you would add PrincipalTag to the condition in your trust policy, is that correct?

[jsimoni]

@peterwoodworth, yes that's correct.