Properly Configure Alexa Skill Id Permissions to Invoke Backend Lambda Function with SAM CLI Template

ask-sam-template.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: Alexa App Hello World Lambda Endpoint

Mappings:
    Variables:
        AlexaSkillKit:
            Id: amzn1.ask.skill.xxxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

Globals:
    Function:
        Timeout: 3

Resources:

    HelloWorldFunction:
        Type: AWS::Serverless::Function
        Properties:
            CodeUri: hello_world/
            Handler: app.lambda_handler
            Runtime: python3.6

    HelloWorldFunctionAskPermission:
        Type: AWS::Lambda::Permission
        DependsOn: HelloWorldFunction
        Properties:
            Action: lambda:InvokeFunction
            EventSourceToken: !FindInMap
                - Variables
                - AlexaSkillKit
                - Id
            FunctionName: !GetAtt HelloWorldFunction.Arn
            Principal: alexa-appkit.amazon.com

Outputs:

    HelloWorldFunction:
        Description: "Alexa Hello World Lambda Function ARN"
        Value: !GetAtt HelloWorldFunction.Arn

    HelloWorldFunctionIamRole:
        Description: "Implicit IAM Role created for Alexa Hello World function"
        Value: !GetAtt HelloWorldFunctionRole.Arn

    HelloWorldFunctionAlexaSkillKitId:
        Description: "Alexa Skill Permitted Lambda Invokation Permissions"
        Value: !FindInMap
            - Variables
            - AlexaSkillKit
            - Id
            

NOTE: If one is using Alexa Smart Home as the needed permissions, the Principal would instead be alexa-appkit.amazon.com