Cloudformation IAM Policy

Question

I am confused how to include a policy in my Cloudformation template to allow

The Cloudformation template below creates a role that allows my Lambda function to be executed. I now need to add a policy that allows the API to execute the Lambda function. From AWS documentation I understand I have to add the following policy but I'm unclear how to append it to the template I have.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "execute-api:Invoke"
      ],
      "Resource": [
        "arn:aws:execute-api:us-east-1:*:a123456789/test/POST/mydemoresource/*"
      ]
    }
  ]
}

This is my current template

  LambdaServiceRole:
        Type: AWS::IAM::Role
        Properties:
          AssumeRolePolicyDocument:
            Version: '2012-10-17'
            Statement:
            - Effect: Allow
              Principal:
                Service:
                - lambda.amazonaws.com
              Action: sts:AssumeRole
          ManagedPolicyArns:
          - "arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole"
          Path: "/"

Answer 1

I believe you'll want the action for for the AssumeRolePolicyDocument to be a list.

LambdaServiceRole:
  Type: AWS::IAM::Role
  Properties:
    AssumeRolePolicyDocument:
      Version: '2012-10-17'
      Statement:
      - Effect: Allow
        Principal:
          Service:
          - lambda.amazonaws.com
        Action: 
          - sts:AssumeRole
    ManagedPolicyArns:
    - "arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole"
    Path: "/"