Implement AWS_IAM Authorizers

[brettstack]

Based on the RFC #781, we need to implement the AWS_IAM Authorizers feature.

Requirements:

1. Implement Transform
2. Add tests
3. Add example(s)

Some code areas to get started for any interested contributors:

1. Add InvokeRole as a valid property of Auth https://github.com/awslabs/serverless-application-model/blob/master/samtranslator/model/api/api_generator.py#L20
2. Add an exception for AWS_IAM DefaultAuthorizer here https://github.com/awslabs/serverless-application-model/blob/master/samtranslator/model/api/api_generator.py#L321
3. Ensure this section is working and only a single sigv4 security definition gets added https://github.com/awslabs/serverless-application-model/blob/master/samtranslator/swagger/swagger.py#L343
4. Add 'sigv4' to securityDefinitions if it's defined as DefaultAuthorizer or if it is specified on any of the Methods https://github.com/awslabs/serverless-application-model/blob/master/samtranslator/swagger/swagger.py#L289
5. Update Integration with credentials https://github.com/awslabs/serverless-application-model/blob/master/samtranslator/swagger/swagger.py#L101

[rhboyd]

Is the idea that it would look something like:

Auth:
  Authorizers:
    AWS_IAM: some:arn:aws:1

and the serverless macro would transform that into specifying AWS_IAM for the auth type and add the policy to the resource policy on the API?

[rhboyd]

or possibly

Auth:
  Authorizers:
    AWS_IAM: NOT_AN_ARN

And the macro would create an IAM Role named NOT_AN_ARN and substitute that Role ARN where applicable in the previous comment?

[brettstack]

@rhboyd check out the RFC #781

[horike37]

Hey @brettstack, I would like to start working on this since this feature is needed for my job.
No problem?

[brettstack]

Absolutely! We look forward to a PR. ❤️

[horike37]

Hey @brettstack, My PR #827 is just ready for review!
Please go ahead 👍 😄 Thanks!

[brettstack]

Thanks @horike37! This has been merged to develop and we'll get it out to production asap.

[horike37]

Great! Can't wait to release 😄

[keetonian]

Released with SAM v1.11.0!