feat: add StepFunctionsCallbackPolicy policy template

[jdg2896]

Issue #, if available

#2193

Description of changes

Adds a new policy template StepFunctionsCallbackPolicy with the necessary permissions for implementing callback patterns.

For more context, I've recently implemented callback patterns with my Step Functions workflow. A Lambda function calls back with the task token along with SendTaskSuccess or SendTaskFailure.

I've originally implemented this (Step Functions - Lambda callback pattern) via SAM Connectors (AWS::Lambda::Function to AWS::StepFunctions::StateMachine), but found the connector policy lacking the necessary permissions for the SendTaskSuccess or SendTaskFailure callbacks.

With connector policies not working for callback patterns, I opted for defining my own policy, which worked.

This is a continuation of a previous attempt to provide a policy template for callback patterns (issue and PR). I've also corrected the Resource scope, which was a requested change that was never resolved in the original PR.

Description of how you validated changes

I validated the changes by updating the translator tests and running make test on Python 3.8.16.

Total test coverage is at 95.73%.

Required test coverage of 95% reached. Total coverage: 95.73%

3961 passed in 267.87s (0:04:27)

Checklist

• [x] Adheres to the development guidelines
• [x] Add/update transform tests
  • [x] Using correct values
  • [ ] Using wrong values
• [ ] Add/update integration tests

Examples?

Please reach out in the comments if you want to add an example. Examples will be added to sam init through aws/aws-sam-cli-app-templates.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[xazhao]

Hello @kshyun28 , For new policy template PR, it has to go through security review which will take some time. We won't be able to merge the PR now.

[jdg2896]

Hello @xazhao, I understand.

If there's anything else required from me (or if the team thinks this is not a valid use case), please let me know.

Thank you for reviewing!

[GavinZZ]

Hi there, just an update on this pull request. We've created the security review internally. It's pending a couple of tasks at the moment. Once the tasks are complete, we will bring it up the security engineer for a final round of review.

[GavinZZ]

Hi @kshyun28, sorry for the long wait! I've some good news to share with you. We've finally gotten security engineer's sign off and I will be merging this PR soon.

[jdg2896]

Hello @GavinZZ, I appreciate all the hard work you and the AWS-SAM team did in order to add this feature.

It's my pleasure making a small contribution to a tool I've used for serverless applications.