Usage plan not supported for implicit APIs

[mcintyre94]

Description:

Usage plans for auth on APIs was added in #1141

Looking at ApiAuth docs (the Auth field on AWS::Serverless::Api objects) - https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-property-api-apiauth.html - the UsagePlan field is present.

But implicit APIs (Api events under AWS::Serverless::Function) - https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-property-function-apifunctionauth.html - are missing that field. So the APIs produced by Lambda functions in SAM don't seem to support this field, which would be useful. Is it possible to support it?

Steps to reproduce the issue:

Add to a SAM template:

  MyFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: lambdas/my-function
      Handler: index.lambdaHandler
      Runtime: nodejs12.x
      Events:
        MyFunctionApi:
          Type: Api
          Properties:
            Path: /my-function
            Method: post
            Auth:
              ApiKeyRequired: true
              UsagePlan:
                CreateUsagePlan: PER_API

Observed result:

When deployed, this API is created, but no usage plan or API key are.

Expected result:

The API is created, with a usage plan and API key - in the same way they would if it was a top-level API object, as described in #1141

[ShreyaGangishetty]

@mcintyre94 for setting UsagePlan for Implicit API please add it in Globals or else UsagePlan can only be used with explicit Apis.